Overview
- The gap before the first number is a deliberate feature that preserves accuracy as the ruler’s edge wears with use.
- Starting the scale a few millimeters in makes the first reading come from a fixed internal mark rather than a dinged corner, which lowers error.
- The empty margin shields the start of the scale from bumps and scuffs, extending the tool’s useful life in classrooms and everyday tasks.
- If the zero mark is worn, users can align the object with another clear mark and subtract that value to get the true length.
- Newer coverage notes standards that tell users to read from the printed zero rather than the edge, a practice also found on tape measures and calipers.