It's a simple way of addressing the difference: 0-indexed "points to" the start of each element. 1-indexed represents the ordinal position.
So to relate to the ruler, the first cm/inch interval is, well, the 1st. But the distance to the start of the first is 0. So if you want to emphasise which numbered interval it is, 1-indexed makes most sense. If you want to emphasise where it starts, or the distance from origin, 0-indexed makes more sense.
It's a simple way of addressing the difference: 0-indexed "points to" the start of each element. 1-indexed represents the ordinal position.
So to relate to the ruler, the first cm/inch interval is, well, the 1st. But the distance to the start of the first is 0. So if you want to emphasise which numbered interval it is, 1-indexed makes most sense. If you want to emphasise where it starts, or the distance from origin, 0-indexed makes more sense.