[sitzkrieg]

calculators dont spit out nonsense learners will not catch

[AnimalMuppet]

Oh yes they do! (Granted, it's either because learners input nonsense, or because they fat-fingered when inputting sane numbers... which I suppose are the same thing when you come down to it.)

[pixxel]

Incorrect inputs and it will. Double-checking source numbers and correct key presses was commonplace.