I noticed the other day that you can type "1+1 sq ft in sq in=" and macOS will helpfully autocomplete the answer: 1,694.0031 square inches. Which is completely wrong. 2 square feet is 288 square inches. It took a few minutes to solve the puzzle of what the hell it is doing.
So take caution trusting Apple's math, which naturally is up to 2x better³—for some value of x.
I had the same issue with a different calculation. The answer was wrong.
I thought it looks weird because I put a space after the = and the autocomplete does not add that.
The order of operations here is quite ambiguous. It’s not obvious even to a human reader how you would expect this to be interpreted.
<expression without units> [<unit> [in <unit>]]
<expression with units> [in <unit>]
Of course the appropriate care must be paid to interpreting "in" correctly as either a unit or a keyword.
Fun puzzle. Spoilers ahead:
It seems it’s considering the first 1, and not the second, to be in square meters. “(1+1) sq ft in sq in” works.
If you type too quick, it misses numbers.
If you type too many times “+” it add too many times
If you try to use it as old standalone calculator, things does not calculate right.
It is hard to clear numbers.
Just so stupid.