Jock -- Just curious as to how you might have acquired this particularly interesting little gem of knowledge ... Did a barley beverage of some sort serve as a catalyst/accelerant to the learning process here??

No alcohol was involved John as I was working at the time.
I was demonstrating the difference between the two types of glass to a trainee in a less than scientific way.
We had a scratched front door glass from a F*rd Mondeo rescued for the glass recycling dumpster which has a compound curve,I placed it facing curve upwards on two wooden blocks on the shop floor and actually managed to invert it with the center nearly touching the ground,a deflection of nearly 3" and when I stepped off it literally bounced back into shape but didn't shatter.
I have to say I was suitably impressed myself.