Have you ever noticed that, on most of the rulersit zero it is not exactly at the end but is often preceded by a small one empty space? It’s such a common detail that we don’t even pay attention to it: yet, after a Spanish user raised the issue in a post on X (visible below), the question became viral.
The answers the most popular ones were, as expected, the most ingenious: there are those who said it was needed “so as not to cut the zero in half” and those who hypothesized it was “reserved for -1”.
The real explanation, however, is much more banal and it deals with a very concrete problem, wear and tear. The angle of a ruler, in fact, is la most exposed part to impacts, rubbing And falls: it bangs against the walls of the case, ends up on the floor, hits the edges of the tables and therefore inevitably tends to wear out or get ruined.
Consequently, if the 0 were placed right on the edge of the ruler, every little sign of wear would result in a measurement error: Even just half a millimeter missing from the end of a ruler would cause a half millimeter inaccuracy in every reading.
Moving the zero sign towards the inside, therefore, the producers create a sort of “sacrificial margin”, a safety zone that allows the instrument to last over time while still remaining precise even if the margin is ruined. The empty space in each ruler is therefore one engineering solution and serves to guarantee greater durability. But also to remember, implicitly, one rule fundamental present in technical drawing manuals since the early twentieth century: to measure correctly you must always start the object from the 0 mark, never from the edge of the ruler.
The problem of wear, among other things, also affects other measuring instruments, such as tape measures: in this case, however, at the end before the 0 there is a tip Of metal or a hook.
