Report for Jim Aitken
Approved stories1
SummaryPerfectly Exquisite

A further alternative was:
Pupil : Sixteen
Mr. MacPherson : You nit!
Pupil : Sorry, sir - sixteen Joules
Here, the amusing similarity between 'unit' (the missing unit of measurement) and the ludicrously mild term of abuse 'You Nit' assured hilarity. *cough* As did said Mr. MacPherson's habit of calling Richard Williams 'Willy Bums'.