**How to effectively use the solver for your own equations**

I
consider the solver model of the hp17bII - hp19bII families the best
there is. It allows you to perform normal calculations, but you still
have the possibility of entering data at any time in on of the
variables.

When using the HP48-hp50 family of calculators, this
is one of the missing features for my daily operation. So I began
exploring alternatives to mimic the behavior of the solver I love the
most.

The typical solver in the HP50g is very useful and gives a
lot of information: a screen with all the fields of the formula with
their current values. However, it does not allow you to continue with
your calculations, and just use the solver keys when needed, like the
17bII.

In the reference manual, there are information about many
hidden menus. One of them is MENU 75. It goes to a submenu where there
are some solver related options.

The first one leads to a soft menu where the keys are the different
variables of the formula stored in 'EQ'. You have a glimpse of the
formula in the upper part of the screen. So, you just need to store the
formula in 'EQ'.

How to automate it just a little bit more?

We can prepare some "programs" that lead to the solver formulas that we want. This is what we did for the financial calculator:

<< 'Formula' 'EQ' STO 75 MENU >>

A
significant difference over the series 17bII solver is that the latter
calculates the value of the variable when you key on it after having
keyed on other variable before. So it knows when to solve.

With
this menu system, you enter the variables the same way, but in order to
solve, you need to left-shift the variable you want to solve for.

Once
you get the idea, you can live quite well with it! Now I use it for
most of the normal daily functions. Actually, it is easier to select the
program by browsing on the variable list, than going through the list
of entered formulas in the 17BII solver.