Trig algorithms on HP RPN?

[MinkLib]

Can someone tell me if the trig algorithms for HP (and other RPN calculators) are all done in radians (behind the scenes). The reason I ask is I've been trying out the Mike Sebastian Forensic test.
It is of course meant to find the underlying chip used, regardless of brand name. But it gives a (very) rough estimation of accuracy, and the results I get using 0.15707 radians are startlingly better than with 9 degrees.

HP-25 degrees 9.0040 error 0.05%
HP-25 radians 8.9999 error 0.00003%

Any Soviet Elektronika programmable RPN (eg B3-34) degrees 9.0881 error 1%
Any Soviet Elektronika programmable RPN (eg B3-34) radians 9.0000 error 0.0003%

Sinclair Scientific radians 8.9381 error 0.7% (no degree mode)

Thanks.