Two Scales - twinx()


I was wanting to use dual scales on my plot and was just running the example code from

I subsequently changed the function Tc to read

def Tc(Tf):

     return Tf

Fully expecting the two scales to track each other perfectly.

I found after zooming the scales did not track each other.

So my question is:

Am I misunderstanding what my change should have done, or is there some error in the example code?

I tried this on win7 64 with:

python 2.7

numpy 1.8.0

matplotlib 1.3.1

Any suggestion welcome.