bchadwick

Thanks rus1bus.
This is very interesting stuff. Agreed that #1 proves that elasticity is not a slope.
Not important for the exam, but just out of curiosity  would like to get your views on #2. The %change is a similar methodology used in deriving the slope of a duration. I think the %change implies a first derivative of the xy function with respect to x. So, I am not entirely convinced that %change in values means that it is not a slope.
The following is from Schweser on one of the definitions of duration:
“…duration is the slope of the priceyield curve at the bond’s current YTM. Mathematically, the slope of the priceyield curve is the first derivative of the priceyield curve with respect to yield…”
Source: Schweser, SS16, page 140
Many thanks for your help!
Cheers