Water pipe minutes and inches is how to calculate?

Pipe size is generally expressed in the nominal inner diameter of the pipe, such as DN25 that the hole diameter of 25mm pipe.

We usually also hear the 4 minutes of pipe, 6 minutes of pipe called. Then 4 points 6 points of the points in the end is what? And how did the name come about?

There are usually several explanations

1. British cents explanation: that an inch is equal to 8 British cents. In fact, there are no cents in the English system

2. 1/8 of an inch is called a cent: this actually also stems from the cents interpretation

3. standard: this is considered to be the rule

4. agreement: this is considered to be the agreement

So what exactly is the interpretation of the cent?

In fact, this minute is the city minute (like we used to use zhang, ruler, inch)

Before the introduction of the metric system of units, we used the city unit, such as zhang, ruler, inch, minute

1 city minute is equal to about 3.33 millimeters

In the first contact with the imperial pipe, how to indicate the size of the pipe? We will certainly take our ruler to measure a measure, the following list of several correspondences, then if you do, must be so called

One point = 3.33 * 1 = 3.33 (one cent pipe is about 3.18)

Quarter = 3.33 * 4 = 13.33 (four cent pipe is about 15)

Sixth = 3.33 * 6 = 20 (six cent pipe is about 20)

Sixth = 3.33 * 6 = 20 (six cent pipe is about) for 20)

Eighth=3.33*8=26.6 (one inch pipe is about 25.4)