HP 50g Graphing Calculator - Manual (Page 789)

Page 27-7
The menu labels for the variable keys are white at first, but change during the
solution process as described below.
Because a solution involves many equations and many variables, the Multiple-
Equation Solver must keep track of variables that are user-defined and not
defined—those it can’t change and those it can. In addition, it keeps track of
variables that it used or found during the last solution process.
The menu labels indicate the states of variables. They are automatically
adjusted as you store variables and solve for variables. You can check that
variables have proper states when you supply guesses and find solutions.
Notice that marks the variables that were used in the last solution—their
values are compatible with each other. Other variables may not have
compatible values because they aren’t involved in the solution.
Undefined all
%ALL% Makes all variables not user-defined,
but does not specify their values.
Solve for all !
%ALL% Creates variables if necessary and
solves for all that are not user-defined
(or as many as possible).
Progress catalog …
%ALL%
Shows information about the last
solution.
User-defined
MUSER Sets states to user-defined for variable
or list of variables on the stack.
Calculated
MCALC Sets states to not user-defined
(calculated result) for variable or list of
variables on the stack