USNO A2.0 "R"

[Michael Koppelman <lolife@bitstream.net>]

I'm sure I could find this somewhere, but I'm wondering how the 
USNO A2.0 "R" compares to the Cousins R. The reason I ask is 
when I use the R magnitudes on the comp stars of the star I am 
working on, they don't really match up. Using the USNO A2.0 R 
magnitudes the difference between my two comp stars should be 
0.7. With my data, using an average of over 200 measurements, 
the difference is 1.2. When you split the difference I get 9.95 
vs. USNO's 10.2 and 11.15 vs. USNO's 10.9.

The stars in question are HD 189797 and GSC 1071-1970.

The other weird part is, using these comp stars I got an average 
of 10.23 on my variable star. TASS gets I~9.2 and V~9.7 at this 
part of the phase. I would have thought that my R would be in 
between the V and I values. I'm wondering if my R comes out so 
dim because I'm using dim USNO magnitudes or something? Are 
there any other good sources for R magnitudes?

Thanks!
Michael