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.