Native mode of trig functions?

[naddy]

I feel like I should be able to tell from the Appendix "Accuracy of Numerical Calculations" in the HP-15C Advanced Functions Handbook—but I can't.

Does the fact that the trig functions are more accurate for real arguments in degrees (and grads) mode than in radians mode imply that the modes use separate algorithms? Or is it due to internal d>r conversion using 13 digit accuracy?