As a form of work or punishment prisoners were made to turn the handle of a handcrank - a totally repetitive and meaningless exercise.
Adults had to turn up to 14,480 revolutions a day (1,800 turns an hour) and juveniles 12,000 revolutions a day (1,500 turns an hour - about one turn every 21/2 seconds). In some gaols, like Leicester, prisoners had to do 2,000 turns to earn breakfast and 5,000 turns to earn dinner.
The handcrank handle only worked one way and its counter could be reset to zero by warders outside the cell. On some models cups scooped sand from inside a box, carried it to the top of the crank wheel, where it fell back to the box bottom. On others pressure on a friction wheel was regulated by warders (nicknamed "screws") who adjusted weights or tightened cogs as they became loose. Later machines were self regulating.
"Prisoner turning the hand-crank."
(Criminal Prisons in London and Scenes of Prison Life by H. Mayhew and J. Binny, first published in 1862.)