Helen, I think he's trying to say there is a difference on the high end of 2 1/2 stops. I counted this one on my fingers (my calculator, the original "Plam") and I still get a 5 stop difference between the readings.
This is why I prefer to use a spot meter in these situations. That, and I don't own an incident meter. tim
P.S. Thanks for taking these readings for us.