If a number like Pi is infinite, how do we know each decimal that is newly calculated is valid?

Question

Not a mathematician here at all so perhaps my question is phrased incorrectly.

Let’s say through thorough testing in reality, we can prove with certainty Pi is correct up until 5 decimal places,

3.14159

The computers that are calculating Pi to an endless degree, how do they validate new values that are calculated as correct and cannot be otherwise?

In: 434

Answer 1

You verify your answer.

Simply put 1+1=2. take a 1 pen, bring in an additional pen. how many pens? 2. Repeat with another item. same answer? Have someone else attempt it. same answer? then 1+1=2.

With Pi, and other irrational numbers. they start the calculation, then attempt the calculation a second, then a third and fourth time,. Mathematicians repeat and if the answer comes back every time with the same answer then we know that the original calculation is correct.