What is the error interval?

When a number is rounded, the Error interval tells us the range of numbers it could have been prior to being rounded.

For Example: 4.8 is rounded to 1 decimal place, so the lowest it could have been is 4.75 and the highest number is could have been is just below 4.85.

So the error interval is between 4.75 (inclusive) and 4.85 (not inclusive) .