Halve
Cut in two; keep the half that holds it; cut again; stop at one.
Twenty versions, five looks, one culprit.
Seen in Ora and Theo Coster (Theora Design), Wie is het? (Guess Who?), 1979
Try it on your work
Take twenty saved versions of a design, one of which is the first to show a fault. Look at the middle one: if it has the fault, keep the earlier half; if not, the later. Halve again. Stop when one version is left.
A long text reads wrong somewhere and you cannot say where. Cover half and read the rest: does it still read wrong? Keep the half that does and cover half of that. Stop at one sentence.
One person picks a word in a dictionary. The other may only open the book at the middle of what is left and ask "before or after this page?". Stop when the page is found.
How it has been used
When something has gone wrong somewhere in a long stretch of work, cut the stretch in two, test which half holds the fault, and cut that half again: the saved versions of a file checked from the middle, the run of prints split into good and bad halves, the recipe changed half its steps at a time. The move forbids checking part by part from the start: every test must split what is left in two.
Where it leads
Grouped under Let me find out what holds up