Generally, there is a factory date. If there is no cover on the back, it is inside the table, and there is a date at the bottom of the table.

When facing the gas meter, the numbers of the three red wheels on the right represent the accurate reading of three digits after the decimal point, which can be read as: 0 1 127888. The three digits of 888 are decimal places, so you don't need to look at this. The fourth place from the right is one, ten, one hundred, one thousand and ten thousand respectively, and the unit is cubic meters.