The traditional wooden ruler had the pervertible properties of the dual-purpose nature so as not to stick out to the [[class]] as only there to [[chastise]] and the durability that you didn't need be partially careful about it break when used as a spanking implement, however as in its primary design usage the wooden measuring edge was prone to denting making flaws for a drawing guide as such have been phased out of typical [[classroom]] usage.
The denting flaw had a workaround of adding a metal edge to the wood. As a spanking implement, this was less useful as a less than perfect [[stroke]] could land slightly turned and his mostly edge-on on the metal side possible causing undesirable [[welts]], [[
The plastic ruler by contrast has all the advantages of cheap, doesn't easily dent, and not only doesn't have the temperature altering it measuring, but their ability to be [[transparent]] actual also makes them the superior choice for accurate measuring. This means they rapidly replaced the traditional wooden one in classrooms once they became cheaply available. However, as a spanking implement, they are prone to snapping. In theory, stronger plastics like [[lexan]] could be used but they're not as cheap and schools that still use [[school corporeal punishments]] are more likely to use a dedicated spanking implement than relay on an obsequious pervertable.