The old man at home said that there are many versions of the perpetual calendar. I don't know which is better and more accurate for normal use.

If the elderly want to use the perpetual calendar APP, I still recommend the ink perpetual calendar. Because the version of the yellow calendar in this perpetual calendar is more accurate, and he can annotate the yellow calendar in vernacular, it will be easier for the elderly to understand. The most important thing is that there is no advertising link in it, so I am not afraid that the old man will accidentally touch it and cause unnecessary operations. I think it's more appropriate.