You can get the individual CD's for $10. That may be a more
economical choice. There is a free open source manual
http://thomasokken.com/free42/42s.pdf that covers some things, but I
could not find the answer to your question in it. I do have the CD
version of the real manual, and it says the following:
"Flags 42 and 43: Angular Mode. The status of flags 42 and 43
determines the angular mode (Degrees, Radians, or Grads). If flag 42
is set (GRAD on), the calculator is in Grads mode. If flag 43 is set
(RAD on), the calculator is in Radians mode. If both flags are clear
(default), the calculator is in Degrees mode."
Another excellent source of advice is the forum at the HP Museum. It
is very active.
http://www.hpmuseum.org/cgi-sys/cgiwrap/hpmuseum/forum.cgi