HP 50g Graphing Calculator - Manual (Page 793)

Page 27-11
Constant? The initial value of a variable may be leading the root-
finder in the wrong direction. Supply a guess in the opposite direction from
a critical value. (If negative values are valid, try one.)
Checking solutions
The variables having a šmark in their menu labels are related for the most
recent solution. They form a compatible set of values satisfying the equations
used. The values of any variables without marks may not satisfy the equations
because those variables were not involved in the solution process.
If any solutions seem improper, check for the following problems:
Wrong units. A known or found variable may have units different from
those you assumed. These are global variables. If the variable existed
before this calculation, then its unit system (SI or English) takes priority. To
correct the units, either purge the variables before solving the equation, or
enter the specific units you want.
No units. If you are not using variables, your implied units may not be
compatible among your variables or with the implied units of constants or
functions. The current angle mode sets the implied units for angles.
Multiple roots. An equation may have multiple roots, and the solver may
have found an inappropriate one. Supple a guess for the variable to focus
the search in the appropriate range.
Wrong variable states. A known or unknown variable may not have the
appropriate state. A known variable should have a black menu label, and
an unknown variable should have a white label.
Inconsistent conditions. If you enter values that are mathematically
inconsistent for the equations, the application may give results that satisfy
some equations but not all. This includes over-specifying the problem,
where you enter values for more variables than are needed to define a
physically realizable problem—the extra values may create an impossible
or illogical problem. ( The solutions satisfy the equations the solver used,
but the solver doesn’t try to verify that the solution satisfies all of the
equations.)