Rulers measure cardinal quantities and not ordinal ones. There is no cardinal numbering scheme that starts at 1, all of them "start" at 0. For ordinal numbering schemes, the symbols are arbitrary anyway and you can start with whatever you want. It's equally valid to start with 1, 0, -1, A, or "aardvark". The only benefit to picking 1 as the start is to make it easier to count with your fingers while picking 0 lets you easily convert an ordinal quantity to a cardinal one.