"gareth" wrote in news:m1agro$srh$1@dont-
email.me:

Square = odds, Triangle = evens

Nope. Both odd. Only when the pulse width ratio becomes significantly
asymmentrical do you get significant occurence of even harmonics in a ramp.
I don't know of a wave that has only even harmonics (short of artificially
contructed ones), but thermionic valves will produce a distortion that has
evens stronger than odds, I think. (I read that somewhere, I've never
measured it).