Compression Ratio

is pie always 3.142

Well, pi actually goes on for thousands of numbers* and there are books filled with, literally, just the value of pi, but that's acceptable for most things. next significant figure would be 3.1416. Depending how accurate you need to be will determine how many decimal places are used. You may remember using 22/7 as an approximation at school, that would work out at 3.142857143... which is pretty darn close at 0.04% difference,

I'm at something of a loss why you felt the need to ask that question, though? There is a story that one of the more ignorant counties in the southern states of America tried to make it an even 3, but there seems to be no evidence it actually happened.

*https://www.google.com/search?client=firefox-b-d&q=what+is+pi%3F - those should answer all your questions.