Can someone explain to me the greatest possible error when finding the maximum and minimum possible lengths of something?? PLEASE!!!

The error can be expressed as units, or as percentage.

Say you have a somewhat accurate ruler, and you measure a board. You find a length of 3m, but the lines on the ruler are rather blurred, so there's a chance of a 2mm error either way.

So, the actual length could be anywhere from 2.998m to 3.002m.

Or, if you're using an electronic device, maybe its specs say that it's accurate to 1%.

In this case, 1% of 3m = 3cm, so the real length could be from 2.97m to 3.03m.