What is written on the keys of an ICL Hand Card Punch 2540

The top three rows are normally numbered 12, 11, and 0 (counting from the top). A punch in row 0 represents the numeral zero, so that's what should be on that key top.

A punch in row 11 represents a hyphen (minus sign) in every card code I know of. Combined with a punch in rows 0 through 9 in the low-order column of a numeric field it means that the amount is negative. So my guess would be to put either "11" or "-" on that key.

A single punch in row 12 is an ampersand in EBCDIC, or a plus sign in many older codes. A 12 overpunch in the low-order column of a numeric field is often acceptable for positive numbers. So "12", "+", or "&" would be reasonable choices, although "&" might be a bit too obscure (or modern!).

I suspect that these three keys would only have a single mark on them. The other characters on the keys for rows 1 through 9 correspond to the codes with none, 12, 11, or 0 overpunches. In your example of the 1 key, a 1 punch by itself represents the numeral 1, 12-1 punches represent the letter A, 11-1 is J, and 0-1 is a slash. Having the four values on the keytops gives a quick guide as to which of rows 12, 11, or 0 to also punch to get any letter of the alphabet (plus the slash).

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