The CPI index is more or less inflation.

Edit the introduction of this paragraph.

CPI (consumer price index), that is, consumer price index, refers to the changing trend and degree of the price level of goods and services consumed by residents in a certain period of time. The change rate of consumer price level reflects the degree of inflation (or austerity) to a certain extent. Generally speaking, CPI is the percentage of commodity price increase in the market. Generally, market economy countries believe that the CPI growth rate is within the acceptable range of 2%~3%, and of course it depends on other data. Too high CPI is always a bad thing. High economic growth rate will increase CPI, but it is definitely not a good thing for the price index to grow faster than the average income of the people, and it is difficult for the average wage to grow faster than 3-4%. [ 1]

Consumer price index (CPI) is a relative number to measure the price level of consumer goods and services for a period of time, and comprehensively reflects the changes of the price level of consumer goods and services purchased by residents. It is an important indicator of national economic accounting, macroeconomic analysis and forecast, and the implementation of overall price level regulation. Consumer price index is widely used as the main indicator to measure inflation in all countries of the world. [2]

The relationship between CPI index and inflation: generally speaking, when CPI increases by more than 3% year-on-year, we call it inflation; When it exceeds 5%, we call it serious inflation. [3]

CPI is a lagging data. The GDP growth of European and American countries has been fluctuating around 2%, and the CPI is also fluctuating between 0% and 3%, while the situation in China is completely different. [ 1]

in China

The national consumer price index (CPI) covers the prices of 262 basic categories of goods and services in 8 categories, including food, tobacco and alcohol, clothing, household equipment and supplies and maintenance services, medical care and personal supplies, transportation and communication, entertainment, educational and cultural supplies and services, and housing. The data comes from 500 cities and counties in 3/kloc-0 provinces (autonomous regions and municipalities) and 63,000 price survey points, including grocery stores, department stores, supermarkets, convenience stores, specialized markets, specialty stores, shopping centers, farmers' markets and service consumption units.

Consumer price index

Xiao Geng, a professor at the School of Public Administration of Tsinghua University and a senior researcher at the Brookings Institution in the United States, believes that by 20 13, the official CPI was not faked, but compared with the actual situation, the error was great, mainly because the statistical system was outdated. As far as the Engel coefficient of 40% is concerned, Xiao Geng thinks that the weight of food is obviously too high. "How many families spend 40% of their money on meals now?" According to Xiao Geng's analysis, the statistics of 20 13 still continue the past pattern, mainly focusing on food, but the living expenditure structure of China people has changed long ago, with buying a house, buying a car and medical care becoming the three major expenditures. [4]

Composition and specific gravity of each part

20 1 1 The latest adjustment is:

1, food 3 1.79%

2, tobacco, alcohol and supplies 3.49%

3. Living in 17.22%

4. Transportation and communication 9.95%

5. Personal articles for medical care 9.64%

6, clothing 8.52%

7, household equipment and maintenance services 5.64%

8. Entertainment, education, cultural goods and services 13.75%

First of all, in order to facilitate comparison, the base period was adjusted. Because the longer the comparison base period, the greater the change in price specifications and quality, and the comparability will decline.

Second, according to the latest business formats, farmers' markets and service consumption units in the selected cities and counties in 20 10, and according to the principles and methods stipulated by the state, new survey outlets were added 13000. 63,000 survey outlets (including grocery stores, department stores, supermarkets, convenience stores, professional markets, specialty stores, shopping centers, farmers' markets and service units, etc.). ) collect CPI prices nationwide.

3. According to the consumption level and habits of local residents, according to the principles and methods stipulated by the state, some representative specifications were updated in time.

CPI rise

Exponential rise

On February 7th, China Academy of Social Sciences released 20112 "Blue Book of Economy" forecast.

The Blue Book points out that China's CPI increase will continue to run at a high level in 20 1 1 year. 20 1 1 Consumer prices rose by an average of 5.6% in the first three quarters. With the gradual weakening of the hikes, the CPI increase in the fourth quarter declined. During the period of 10, the CPI decreased from 6. 1% in September to 5.5%. According to the situation of the whole year, the Blue Book predicts that the annual CPI increase of 201/kloc-0 may reach about 5.5%. In 20 12, the increase of the overall price level shows a downward trend, and it is estimated that the CPI will increase by 4.6% in 20 12.

check against the authoritative text

There is no monthly revision. The annual change will come out when the GDP data of February 1 month is released. The revision can be traced back to five years ago.

meaning

The purpose of compiling consumer price index is to understand the basic situation of price changes all over the country, analyze and study the impact of price changes on social economy and residents' life, meet the needs of governments at all levels to formulate policies and plans and carry out macro-control, and provide reference and basis for national economic accounting.

Combined with the employment situation report (non-agricultural), the consumer price index (CPI) has become another hot economic indicator that has been carefully studied in the financial market. The reason for its concern is obvious: inflation affects everyone, it determines the cost of consumers to buy goods and services, affects the operating costs of enterprises, greatly damages the investment of individuals or enterprises, and affects the quality of life of retirees. Moreover, the prospect of inflation is conducive to the establishment of labor contracts and the formulation of government fiscal policies.

What exactly is the consumer price index? It measures the average change of retail prices of more than 200 kinds of goods and services over time. These more than 200 kinds of goods and services are divided into 8 categories. When calculating the consumer price index, each category has a weight that can show its importance. These weights are determined by investigating the products and services purchased by thousands of families and individuals. The weights are revised every two years to make them conform to people's changing preferences.

20/kloc-a new statistical method of CPI in 0/2 years

In order to better adapt to China's economic and social development and the changes in the consumption structure of urban and rural residents, and ensure the scientificity and accuracy of CPI calculation, we have made routine adjustments to the CPI survey plan, involving the adjustment of comparison base period, weight composition, survey outlets and representative specifications.

1. Starting from 2011,China's CPI began to calculate the price index series based on 20 10. This is the second routine change in the base period since 200 1 calculated the CPI fixed base price index. The first base period is 2000, and the second base period is 2005. For comparison, the base period has been adjusted. Because the longer the comparison base period, the greater the change of price specifications, and the comparability will decline. Choosing 0 to 5 years as the comparative base period for calculating CPI is to keep the same period with the five-year plan for national economic and social development in China, which is convenient for data analysis and use.

Second, according to the survey data of urban and rural residents' consumption expenditure in 20 10 and the statistical data of relevant departments, the weight composition of CPI was adjusted accordingly according to the system regulations. Among them, residential category decreased by 4.22 percentage points, food category decreased by 2.2 1 percentage point, alcohol and tobacco category decreased by 0.5 1 percentage point, clothing category decreased by 0.49 percentage point, household equipment and services category decreased by 0.36 percentage point, medical care and personal articles category decreased by 0.36 percentage point, transportation and communication category decreased by 0.05 percentage point, and entertainment, education, cultural goods and services category decreased.

3. According to the latest business formats, farmers' markets and service consumption units in the selected cities and counties in 20 10, and according to the principles and methods stipulated by the state, the number of survey outlets was increased by 13000. 63,000 survey outlets (including grocery stores, department stores, supermarkets, convenience stores, professional markets, specialty stores, shopping centers, farmers' markets and service units, etc.). ) collect CPI prices nationwide.

Four, the selected survey cities and counties according to the local residents' consumption level, consumption habits, in accordance with the principles and methods prescribed by the state, some representative specifications were updated in time.

Consumer price index

in the U.S

compose

The consumer price index (CPI) in the United States is divided into eight categories, including food, wine and beverage, housing, clothing, education and communication, transportation, medicine, health, entertainment, and other goods and services. The market sensitivity is very high. In the United States, the consumer index is released by the Bureau of Labor Statistics at 8: 30 a.m. Eastern Time. Published in the second or third week of the reporting month. There are two different consumer price indexes: one is the consumer price index of employees, which is called CPI-W for short. The second is the urban consumer price index, referred to as CPI-U.

CPI is a lagging data, but it is often an important reference index for market economic activities and government monetary policy. CPI stability, full employment and GDP growth are often the most important social and economic goals. However, from the reality of China, the stability and importance of CPI are not as authoritative as the developed countries think, and the economic activities of the market will be adjusted according to the changes of CPI.

Impact on exchange rate

The effect of inflation on the dollar is not clear. Usually, in a healthy economic expansion, raising the interest rate of the US dollar can make the US dollar more attractive. If the rise in interest rates mainly comes from the rise in inflation, it will hurt the dollar. The high inflation rate has damaged the value of dollar investment held by foreigners, so the continuous rise of CPI has a negative impact on the dollar.

Foreign exchange traders are also sensitive to other nuances. For example, traders in the foreign exchange market believe that the Federal Reserve has acted quickly and flexibly to control inflationary pressure, and the dollar may maintain its value or even appreciate.

Edit the calculation formula of this paragraph.

The calculation formula of CPI is

CPI= (the value of a group of fixed commodities at current price/the value of a group of fixed commodities at base price) × 100%. The weight is calculated according to the weighted arithmetic average index formula, that is, K = σ kW/σ W, and the weight is w, where the molecular k in the formula is the single index of various sales.

CPI shows how much it costs to buy a representative group of goods today than at some time in the past. For example, if the average family in a country spends 1995 a month to buy a group of goods in 800 yuan, and the cost of buying this group of goods in 2000 is 1000 yuan, then the consumer price index of the country in 2000 is.

(Based on1995) CPI =1000/800×100% =125%, which means that it has increased (125%-100%).

In our daily life, we are more concerned about the inflation rate, which is defined as the percentage change of the price level from one period to another. The formula is

t =(Pt—P(t- 1))/P(t- 1)，

Where, T is the inflation rate of period T, and Pt and P(t- 1) represent the price levels of period T (representing the reporting period) and period t- 1 (representing the base period) respectively.

If the above-mentioned consumer price index is used to measure the price level, then the inflation rate is the percentage of changes in the consumer price index in different periods.

For example, if the consumer price index of an economy rises from 100 last year to 1 12 this year, then the inflation rate in this period is t = (112-100)//kloc-.

The current CPI index in China is calculated according to the previous year (100), not a certain time in history. See the website of the National Bureau of Statistics for details.

Edit the core CPI of this paragraph

The so-called core CPI refers to the consumer price index after excluding the product prices that are greatly affected by climate and seasonal factors. By 20 13, the core CPI has not been clearly defined in China, and the core CPI in the United States is the consumer price index excluding fuel and food prices. This method was first put forward by American economist Robert J Gordon in 1975. The background is that in 1974-1975, due to the impact of the first oil crisis, there was a big inflation in the United States. At that time, the rise in consumer prices was mainly affected by the rise in food prices and energy prices. At that time, many economists believed that the rise of food and energy prices in the United States was mainly affected by supply factors and less by demand. Therefore, the method of deducting food and energy price changes from CPI to measure price level changes is put forward. Starting from 1978, the Bureau of Labor Statistics of the United States began to announce the rising rate after excluding food and energy prices from the consumer price index and producer price index (PPI). However, even in American economic circles, there is still a big debate on whether food and energy prices should be deducted from CPI to judge the price level, and there are many opponents.

Edit this part of China data.

CPI(%) Consumer Price Index Data Source: National Bureau of Statistics 20 10-20 12 National CPI 20 1 July 201June 20/July 20/kloc-0.

CPI Index of China in 20 12 years

65438+ October

The national consumer price level rose by 4.5% year-on-year.

20 1 February 9th, the National Bureau of Statistics released1month macroeconomic data. 20 12 1 month, the national consumer price level rose by 4.5% year-on-year. Among them, cities rose by 4.5% and rural areas rose by 4.6%; Food prices rose 10.5%, and non-food prices rose10.8%; The price of consumer goods rose by 5.5%, and the price of service items rose by 2.2%. The national consumer price level rose by 1.5% month on month. Among them, the urban increase was 1.5%, and the rural increase was1.5%; Food prices rose by 4.2%, and non-food prices rose by 0.2%; The price of consumer goods rose by 1.8%, and the price of service items rose by 0.8%.

February

The national consumer price level rose by 3.2% year-on-year.

2065 438+02. 3. 9 The National Bureau of Statistics announced that in February, the national consumer price level rose by 3.2% year-on-year. Among them, cities rose by 3.2% and rural areas rose by 3.2%; Food prices rose by 6.2%, while non-food prices rose by1.7%; The price of consumer goods rose by 3.9%, and the price of service items rose by 1.5%. The national consumer price level rose by an average of 3.9% year-on-year 2011.

In February, the national consumer price level decreased by 0. 1% month on month. Among them, the city decreased by 0. 1%, and the countryside decreased by 0.1%; Food prices fell by 0.3%, and non-food prices were flat; The price of consumer goods decreased by 0. 1%, and the price of service items decreased by 0.2%.

March

The national consumer price level rose by 3.6% year-on-year.

20 12 On April 9, the National Bureau of Statistics announced that in March, the national consumer price level rose by 3.6% year-on-year. Among them, cities rose by 3.6% and rural areas rose by 3.6%; Food prices rose by 7.5%, while non-food prices rose by1.8%; The price of consumer goods rose by 4.4%, and the price of service items rose by 1.5%. In the first quarter, the national consumer price level rose by 3.8% year-on-year .2011.

In March, the national consumer price level rose by 0.2% month on month. Among them, cities rose by 0.2%, and rural areas rose by 0.1%; Food prices rose by 0.2%, and non-food prices rose by 0.2%; The price of consumer goods rose by 0.3%, and the price of service items was flat. [5]

April

The national consumer price level rose by 3.4% year-on-year.

From April 2065438 to April 2002, the national consumer price level rose by 3.4% year-on-year. Among them, cities rose by 3.4% and rural areas rose by 3.3%; Food prices rose by 7.0%, while non-food prices rose by1.7%; The price of consumer goods rose by 4. 1%, and the price of service items rose by 1.7%. From June to April, the national consumer price level rose by 3.7% on average, with 20 1 1 in the same period.

In April, the national consumer price level decreased by 0. 1% month on month. Among them, the city was flat (the fluctuation range was 0) and the rural area decreased by 0.2%; Food prices fell by 0.9% and non-food prices rose by 0.3%; The price of consumer goods fell by 0.3%, and the price of service items rose by 0.5%. [6]

May

The national consumer price level rose by 3.0% year-on-year (note: the year-on-year increase hit a 23-month low). Among them, cities rose by 3.0% and rural areas rose by 2.9%; Food prices rose by 6.4%, while non-food prices rose by1.4%; The price of consumer goods rose by 3.6%, and the price of service items rose by 1.7%. The average national consumer price level increased by 3.5% compared with 20 1 1 in the same period.

In May, the national consumer price level dropped by 0.3% month on month. Among them, the city decreased by 0.3% and the rural area decreased by 0.3%; Food prices fell by 0.8%, while non-food prices were flat (fluctuation range was 0); The price of consumer goods decreased by 0.4%, and the price of service items increased by 0. 1%.

June

The national consumer price level rose by 2.2% year-on-year. Among them, cities rose by 2.2% and rural areas rose by 2.0%; Food prices rose by 3.8%, while non-food prices rose by1.4%; The price of consumer goods rose by 2.3%, and the price of service items rose by 1.9%. In the first half of the year, the national consumer price level rose by 3.3% over the same period of 20 1 1.

In June, the national consumer price level dropped by 0.6% month on month. Among them, the city decreased by 0.6% and the rural area decreased by 0.5%; Food prices decreased by 1.6%, while non-food prices remained flat (fluctuation range was 0); The price of consumer goods fell by 0.9%, and the price of service items rose by 0.3%. [7]

July

According to the general market expectation in 20 12, the CPI announced on August 9, 20 12 will continue to slow down to a new low in the year, and the easing of price pressure will also give the government more energy to revitalize the real economy. Macro data in July is expected to be released today, and CPI is expected to hit a new low in the year. It is estimated that the year-on-year increase of CPI in July will decrease from 2.2% in June to 1.5%. The implied seasonally adjusted month-on-month growth rate decreased from -0.5% in June to -2. 1%. [8]

According to the data of the National Bureau of Statistics, in July 20 12, the national consumer price level rose by 1.8% year-on-year. Among them, the urban increase was 1.9%, and the rural increase was1.5%; Food prices rose by 2.4%, while non-food prices rose by1.5%; The price of consumer goods rose by 1.7%, and the price of service items rose by 2.0%. The average national consumer price level increased by 3. 1% over the same period of 201. It is reported that this is the first time that the CPI increase has fallen below 2% in two and a half years.

In July, the national consumer price level rose by 0. 1% month on month. Among them, the city rose by 0. 1%, and the countryside was flat (fluctuation range was 0); Food prices fell by 0. 1%, while non-food prices rose by 0.2%; The price of consumer goods decreased by 0. 1%, and the price of service items increased by 0.6%. [9]

In August, the national consumer price level rose by 2.0% year on year. Among them, the city rose by 2. 1% and the countryside rose by1.8%; Food prices rose by 3.4%, while non-food prices rose by1.4%; The price of consumer goods rose by 2. 1%, and the price of service items rose by 2.0%. From June to August, the national consumer price level rose by 2.9% on average. [ 10]

Bureau of Statistics: In September, CPI rose 1.9% year-on-year, and PPI hit a 35-month low.

From 2065438 to September 2002, the national consumer price level rose by 1.9% year-on-year. Among them, cities rose by 2.0%, and rural areas rose by1.7%; Food prices rose by 2.5%, while non-food prices rose by1.7%; The price of consumer goods rose by 1.8%, and the price of service items rose by 2.3%. From June to September, the national consumer price level rose by 2.8% on average, 20 1 1.

According to the National Bureau of Statistics, CPI 5438+00 increased by 1.7% year-on-year in June, and the innovation was low [1 1].

Source: National Bureau of Statistics 2012-1-09 09: 30: 00.

20 12 10, the national consumer price level rose 1.7% year-on-year. Among them, the urban increase was 1.8%, and the rural increase was1.5%; Food prices rose 1.8%, and non-food prices rose1.7%; The price of consumer goods rose by 1.5%, and the price of service items rose by 2.3%. 1- 10 on average, the national consumer price level increased by 2.7% compared with 20 1 1 in the same period.

According to the data of the National Bureau of Statistics, the CPI in June 5438+065438+ 10 increased by 2.0% year-on-year.

20 12,110, the national consumer price level rose by 2.0% year on year. Among them, the city rose by 2. 1% and the countryside rose by1.9%; Food prices rose by 3.0%, while non-food prices rose by1.6%; The price of consumer goods rose by 1.9%, and the price of service items rose by 2.3%. 1- 1 1 on average, the national consumer price level rose by 2.7% over the same period of 20 1 1. [ 12]

According to the data of the National Bureau of Statistics, the CPI rose by 2.5% in June 5438+February.

From 20 12 to 12, the national consumer price level rose by 2.5% year-on-year. Among them, cities rose by 2.5% and rural areas rose by 2.5%; Food prices rose by 4.2%, while non-food prices rose by1.7%; The price of consumer goods rose by 2.5%, and the price of service items rose by 2.5%. In 20 12, the national consumer price level rose by 2.6% over the previous year. [ 13]

According to the National Bureau of Statistics, the CPI rose by 3.2% year-on-year in February.

From February 2065438 to February 2003, the national consumer price level rose by 3.2% year-on-year. Among them, cities rose by 3.2% and rural areas rose by 3.3%; Food prices rose by 6.0%, while non-food prices rose by1.9%; Consumer goods prices rose by 3.3%, and service prices rose by 3. 1%.

In February, the national consumer price level rose by 1. 1%. Among them, the urban growth rate is 1. 1%, and the rural growth rate is1.0%; Food prices rose by 2.7%, and non-food prices rose by 0.2%; Consumer goods prices rose by 1.2%, and service prices rose by 0.8%. [ 14]

From 2065438 to March 2003, CPI increased by 2. 1% year-on-year.

20 13 March, the national consumer price level rose by 2. 1% year-on-year. Among them, cities rose by 2.0% and rural areas rose by 2.2%; Food prices rose by 2.7%, while non-food prices rose by1.8%; Consumer goods prices rose by 1.7%, and service prices rose by 3. 1%. [ 15]

Bureau of Statistics: CPI rose by 2.4% in April of 2013.

In April 20 13, the national consumer price level rose by 2.4% year-on-year. Among them, cities rose by 2.4% and rural areas rose by 2.4%; Food prices rose by 4.0%, while non-food prices rose by1.6%; Consumer goods prices rose by 2.2% and service prices rose by 2.9%. The national consumer price level rose by 2.4% on average compared with the same period of last year [16].

CPI rose slightly in May compared with April (2.4%).

Affected by the fall in vegetable prices and the hikes, many institutions predicted that the CPI in May would rebound slightly from April (2.4%), with an increase of about 2.4%-2.5%. Considering that the economic recovery is weak and the ex-factory price index of industrial producers continues to be sluggish, it is expected that the CPI will increase by less than 3% year-on-year. [ 17]

Since May, the national vegetable prices have dropped significantly. According to the monitoring of the Ministry of Commerce, from May 20th to 26th, the average wholesale price of 18 vegetables decreased by 5.2% compared with the previous week. However, the price of meat has increased to varying degrees, and the wholesale price of pork has increased by 1. 1% compared with the previous week, ending the continuous downward trend since mid-February. In this regard, the Bank of Communications (market, capital, stock bar, consultation) report predicts that compared with April, the month-on-month increase in food prices may drop by about 0.5 percentage points. At the same time, the recent non-food prices are basically stable, and the year-on-year increase is basically the same as that in April. In addition, the hikes in May increased slightly by 0.25 percentage points. Based on comprehensive judgment, it is estimated that the CPI will increase by about 2.5% in May. Zhu Baoliang, director of the Macroeconomic Forecasting Department of the State Information Center, said that considering that the current economic recovery is still weak and the PPI data continues to be sluggish, there are still few factors supporting the CPI increase in the short term, but the rebound of pork prices needs attention and may have a certain impact on prices.

The CPI increase in June may rebound to around 2.5%.

According to the monitoring of the Ministry of Commerce, from June 17 to June 23, the prices of edible agricultural products in 36 large and medium-sized cities nationwide fell slightly, and the prices of means of production fell for six consecutive weeks. [ 18]

Analysts said that food prices will remain basically stable in June, but from the perspective of non-food prices and hikes, CPI rebounded in June, and the year-on-year increase is expected to rebound to around 2.5%.

Statistics Bureau: In June, the overall consumer price level rose by 2.7% year-on-year.

From June 2065438 to June 2003, the national consumer price level rose by 2.7% year-on-year. Among them, cities rose by 2.6% and rural areas rose by 2.8%; Food prices rose by 4.9%, while non-food prices rose by1.6%; Consumer goods prices rose by 2.6% and service prices rose by 2.7%. In the first half of the year, the national consumer price level rose by 2.4% compared with the same period of last year. [ 19]

Statistics Bureau: In August, the national consumer price level rose by 2.6% year-on-year.

In August of 20 13, the national consumer price level rose by 2.6% year-on-year. Among them, cities rose by 2.5% and rural areas rose by 2.9%; Food prices rose by 4.7%, while non-food prices rose by1.5%; Consumer goods prices rose by 2.5% and service prices rose by 2.7%. From June to August, the national consumer price level rose by an average of 2.5%. [20]

Edit the meaning of this paragraph

1. Reflect the inflation situation: the severity of inflation is reflected by the inflation rate, which shows the continuous rise of commodity prices in a certain period of time. The inflation rate is generally expressed by the consumer price index.

Inflation rate = (reporting period consumer price index-base period consumer price index)/base period consumer price index X 100%

2. Reflect the change of currency purchasing power: Currency purchasing power refers to the quantity of consumer goods and services that can be purchased by unit currency. When the consumer price index rises, the purchasing power of money decreases; On the contrary, it will rise. The reciprocal of the consumer price index is the purchasing power index of money.

[[Monetary purchasing power index ]] = (1/ consumer price index) X 100%

3. Reflect the impact on employees' real wages: the rise of consumer price index means the decline of real wages, and the decline of consumer price index means the increase of real wages. Therefore, the consumer price index can be used to convert nominal wages into real wages, and its calculation formula is as follows

[[Real Wage]] = Nominal Wage/Consumer Price Index

CPI (cost-effective Idex), cost-effective index. Used for earned value management, CPI=EV/AC.

China Power Investment Group Corporation

China Power Investment Corporation was established on February 29th, 2002 (2002) No.65438. It is a large-scale state-owned backbone enterprise established on the basis of some enterprises and institutions of the former State Power Company. The assets of the group company are distributed in 28 provinces, municipalities, autonomous regions, Hong Kong, Macao and other places, mainly engaged in the development, investment, construction, operation and management of power supply, and organizing the production and sales of electricity (heat).

Edit this piece of computer science

Computer performance index

CPI (number of cycles per instruction): The number of clock cycles (reciprocal of clock frequency) required to execute an instruction.

Calculation method

Seconds: Seconds.

Instructions per second: The number of instructions executed per second.

F: main frequency

MIPS: millions of instructions per second, that is, the number of instructions executed per unit time.