I've got an unusual problem with the ABS (absolute value) function in Excel 2002 SP 3 running on Windows XP Home SP 2.

A cell in my worksheet performs this simple calculation: ABS(SUM(E37:J37)-SUM(K37:M37)). The calculation should normally result in a value of zero. If the calculation results in anything other than zero, my worksheet will alert me to that fact.

Something funny was going on. The cell was showing a value of zero, but my worksheet was still alerting me that the cell was something other than zero.

From Tools Formula Auditing Evaluate Formula I made this startling discovery:

The calculation evaluates to: ABS(12,182.23 - 12,182.23), which in turn does NOT evaluate to ABS(0). Instead, it evaluates to ABS(-1.81898940354586E-12)!

What the...where did -1.81898940354586E-12 come from? Have I done something wrong?

Steven