I'm probably way behind the times, but I have found a mathematical error with Excel that could be problematic in developing calculation spreadsheets:
Excel's order of operations places negation ahead of exponentiation. This gives the following results:
=(3+6)^2 gives 81 instead of 81
=5^2 gives 25 instead of 25
This may seem minor, but try this on for size  try typing this into Excel:
=5^25^2 gives 0
This doesn't follow with what's above, even though it is correct.
Furthermore, typing:
=5^25^2 gives 0 as well!!!
Confused yet?
Clearly Microsoft attempted to make it easier to enter formulas figuring that when someone wanted to square 9 that it would be easier to type just 9^2 instead of the correct (9)^2. That's commendable, but it is flat out WRONG!
If you look under help, and find their order of operations, they even spell out that they place negation above percentages, exponentiation and multiplication. Excuse me, but the last time I checked, negation IS multiplication (multiplying by 1) and belongs in the multiplication spot WHERE IT HAS BEEN FOR CENTURIES!!!
Sorry about the rant, but it comes from building a large calculation sheet and consistently getting wrong answers from it. After a hairpulling debugging exercise, I traced it to this little Microsoft nuance.
Please keep this in mind when building calculation spreadsheets in Excel...
