Why is my rounding bugging?

Sure let me call my hacker friend to get into your computer and know what you mean instead of you giving is the details!

That is me being a jerk but honestly you aren't putting effort to help, you said "decrease decimal function", there are literally over a dozen rounding functions, not even counting other features, here is a some https://exceluser.com/1837/overview-of-excels-rounding-functions/

I'm going to assume you mean the two icons on the home tab, this is just a way to show less of the number BUT it is still there, the reason it is inconsistent would be due to floating points in computers, here is a link about it if interested: https://en.m.wikipedia.org/wiki/Floating-point_arithmetic

But honestly, i think it is VERY unlikely that it would happen to you with 2.45 but I could be wrong.

You can increase precision on option IIRC, but to avoid this, i suggest to just use proper functions like rounddown().

/r/excel Thread