50g

Assuming that you're also lumping the HP-written Advanced User's
Reference Manual (AUR) in the "NOT well written" category, have you
looked at the documentation section of hpcalc.org
(http://www.hpcalc.org/hp49/docs/)?  Most of the documentation there
is written for the 49g, but the 50g is essentially the same from the
user's perspective.

If you haven't yet looked at the AUR, it can be downloaded from HP at:
http://bizsupport2.austin.hp.com/bc/docs/support/SupportManual/c02836298/c02836298.pdf