Sometimes the diagonal shows up as 0 and u have to go back and recalculate.
Other times the diagonal rounds off! I checked this ‘rounding’ against iPhone scientific (horizontal position) calculator a2+b2=c2 (then sq root c2) and this app if off sometimes. It’s like playing Russian Roulette. Developer ghosted on it years ago and has not even submitted a privacy policy either.
Beware of basing any given measurements on real world applications as it could be costly.