Often programmers first wrote their program out on special forms called coding sheets, taking care to distinguish the digit zero from the letter "O", the digit one from the letter "I", eight from "B", two from "Z", and so on using local conventions such as the "slashed zero". These forms were then taken by keypunch operators, who using a keypunch machine such as the IBM 026 (later IBM 029) punched the actual deck. Often another key punch operator would then take that deck and re-punch from the coding sheets – but using a "verifier" such as the IBM 059 that simply checked that the original punching had no errors.