spotlight math calculation precision 0 = 1E-29?
Clearly it’s a bug if you believe the exact math should match. It’s probably also a feature since the math library chosen was likely chosen to be fast and small for the math it needs to do and not scientific accuracy for calculating a moon landing.

This sort of rounding errors happens all the time, especially if you’re sloppy or don’t implement a guard digit for “small numbers” like 65k. All math libraries make approximations when they encode values, so the bits sometimes matter when you are checking for something that’s very close to zero. In your example the two large numbers aren’t perfectly represented and you get a very insignificant rounding error that doesn’t cancel perfectly when the subtraction happens in one case but not the other. The 1e-29 should be rounded to zero IMO unless the goal is to introduce people to this concept.

When you need to be precise, use PCalc or another calculator that handles precision and rounding properly.

Also, if you take 1E-29 of the weight of the earth, that’s just under 60 mg. If you were estimating the mass of the earth, you’d be of by more than a snowflake and less than a grain of sand. This quite literally is the proverbial “making a mountain out of a mole hill”.


http://m.wolframalpha.com/input/?i=1e-29+*+weight+of+earth


That being said, if you like math or computers, this is very cool, since it exposes the internal representation of a number and you see how an approximation can cause rounding errors for not that very large numbers in this case. There are legendary (to engineers and programmers at least) books devoted to numerical recipes and tricks to do quick and accurate calculations when you don’t bring along a perfect math library.