In this MoHPC, you can read the next in the 32S page:

The HP-32S featured to the first RPN solver. The HP-34C had introduced the first built-in root-finder which could solve for f(x) = 0 expressed as an RPN program. To use the root finder the user wrote a function that accepted x, and left f(x) in the X register. The RPN Solver on the HP-32S allowed the user to enter a program which accepted multiple variables and computed f(a, b, c, ...) = 0. After entering a single program, the user could solve for any variable.

So, solve for ANY variable, is "the new" of the 32S/32SII/42S solver when comparing to the 34/15C solver.

I don't know if this is well known for the 15C users, but I'm amazed: take a look at this post of Karl Schneider (5 Mar 2003, 12:45 a.m.):

http://www.hpmuseum.org/cgi-sys/cgiwrap/hpmuseum/forum.cgi?read=29015

This trick let us to use the "old solver" like the "new solver".

I've tried it with two simple ecuations: ideal gas and mechanic energy. It works the same than in the 42S!!

Thanks again, Karl.

Raul