The Results of my Xover Experiement was somewhat surprising!

I Submitted 4 Coins graded by CGS-UK and 1 each from NNC and ICG with the instructions to grade as NGC see fit.

The main aim was to help calibrate the 70 Point Sheldon Scale used by NGC and the 100 Point Scale used CGS-UK. Prior to submission I had calibrated the main grades as follows:

CGS-UK EF70 = MS60

CGS-UK EF65 = AU58

CGS-UK EF60 = AU55

CGS-UK VF55 = AU53

CGS-UK VF50 = AU50

And here are the Results of my TPG Xover Submissions:

1) 1817 George III ICG-AU58 = NGC AU53 (Two Whole Grades!)

2) 1822 George IV CGS-UK VF50 = NGC XF40

3) 1830 George IV CGS-UK VF55 = NGC XF45

4) 1842 Victoria CGS-UK EF70 = NGC AU58 (Unlucky - expected an MS Grade)

5) 1853 Victoria CGS-UK EF65 = NGC AU55

6) 1871 Victoria NNC-MS64 = NGC MS62

Conclusion:

I had always thought the CGS grades to be very harsh, but the NGC results suprised me as they proved to be tougher that I had expected by about 1 grade in the upper EF/AU range and 2 grades in the lower VF/XF-AU range. A perfect calibration between CGS just isn't possible, but my view has been largely reinforced and refined at the same time. As a rough rule of thumb, you can take around 15% off the CGS Grades to get your Sheldon Grades. Example EF65 -15% (~10 points) = AU55

As for NNC and ICG, both were (in comparision to NGC) overgraded by 2 whole grades! I've got an ANACS coin to do next, it will be interesting to see how that turns out!