An Excel math question

Hi, 1st time on this forum in desperation for help.

I have a spreadsheet which does a number of very simple calculations, but for a particular set of numbers, seems to lose the plot. I have a simplification of the problem here if you could look at it.

In A1 place number 7.02
In B1 place number 7.07
In C!, calculate the difference between A1 & B1 ( =A1-B1)
In D1, place number 0.05 ( this will be a limit that C1 becomes reportable)
In E1, do calculation. =IF(ABS(C1)>D1," out of calibration","")

My problem is that the calculation works for all values placed into A1 & B1 except for the above example. In the example shown, calculation in C1 = D1, but fails. For any other values of A1 & B1 which result in C1=D1, calculation works.
Am I going mad?
Thanks.....Peter

No, you're not going mad. You've fallen prey to Excel precision issues.

If you click on the cell with your problem formula and click on the Evaluate Formula icon (Formula Auditing toolbar), step through the formula...you will see that Excel considers the difference between the two values to be -0.050000000007. So, if you ABS() that value, it is slightly greater than 0.05.

Round your math to specific decimals to eliminate the precision oddities.

=IF(ROUND(ABS(C1),2)>D1,"out of calibration")

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