I’ve seen a lot of rulers that actually don’t have a mark at 0 and instead go right to the edge as 0. Typically they are worn down, being made of wood, so the accuracy of the first inch is dubious. To ensure the distance is correct, sliding the ruler down one unit is a good idea. So, my ruler starts at 0 but my measurements start at 1.
I’ve seen a lot of rulers that actually don’t have a mark at 0 and instead go right to the edge as 0. Typically they are worn down, being made of wood, so the accuracy of the first inch is dubious. To ensure the distance is correct, sliding the ruler down one unit is a good idea. So, my ruler starts at 0 but my measurements start at 1.
That’s why decent rulers have a 0 and a margin: