Harmonics. In the old days, the "first harmonic" was twice the fundamental. Then everyone realised what a load of shite that was and started calling twice the fundamental frequency, the "second harmonic", thrice, the "third harmonic" etc. Everyone realised that made more sense by a long way. I therefore ask, why the fuck haven't we done something similar with centuries? The 18th Century is the 1700s -> The 19th Century is the 1800s -> The 20th Century is the 1900s -> etc. It's bullshit.