Huh, until now I've only ever thought of "number cruncher" as a euphemism for "processes numbers rapidly like a creature crunching through food". But, now you

Huh, until now I've only ever thought of "number cruncher" as a euphemism for "processes numbers rapidly like a creature crunching through food". But, now you say this ... early 'computers' (eg adding machines) of course did have teeth (they used mechanical gears) and would literally be 'number crunchers' and so would fit a description of "crunches numbers with it's teeth" as a literal term. Now, a number cruncher in UK English is used to refer to a person, like an accountant: I suppose in the past they crunched numbers using mathematical machines (analogue calculators). Also, of note is that originally a 'computer' was a job role of someone operating a mathematical machine. Obviously then a 'computer' became the machine, and it still 'crunched numbers' except it did it silently using transistors. It sounds like that textbook was not wrong but perhaps just needed explanation.