HP 48GX Solve Equation - Help! Can't remove unit.

[FilmLover451]

I'm fairly new to the HP48GX and am working my way through the manuals. I have a problem with Solve Equation. I can enter or choose the equation but when I try to enter a starting value for the variable (X) the calculator adds a unit to whatever number I enter. For example, if I enter 2 this gets converted to 2_m. As a result, when I try to solve I get the error "Bad Guess". I've tried everything to remove that unit but it won't go away.

A few days ago this worked fine. Since then I worked through the manual section about units and experimented with them. That seems to have changed a setting somewhere, or maybe created a global variable. I've tried CLTEACH and I've tried purging the variables; neither has worked.

Can anyone suggest a solution? Any ideas welcome.

[Joe Horn]

> I have a problem with Solve Equation.

If you're referring to the Equation Library solver (not the shift-7 solver), then you must've accidentally turned on the Units option; just press right-shift 3, then press the C key to turn UNITS off. OR you can set flag 61 (type 61 SF and press ENTER), which has the same effect.

Hope that helps!

-Joe-

[FilmLover451]

Thanks Joe. It isn't the Equation Library; it's the shift-7 solver. I've just discovered that in fact I'm only getting this problem with one equation. Others are behaving correctly. The RATFUNC equation in the TEACH mode files is the only one which is insisting on adding a unit to X. This is a bit strange as I'm sure that previously I was getting this with other equations including those I'd typed in (rather than loaded from memory) though I may be wrong about that being a newbie on this beast. This means it's not a serious problem though I'd still like to know how to switch the units off for future reference. Does that flag setting work only for the Equation Library or is it a more general thing?

Cheers for the help.

Gill

[Joe Horn]

> It isn't the Equation Library; it's the shift-7 solver. I've just discovered that in fact I'm only getting this problem with one equation. Others are behaving correctly. The RATFUNC equation in the TEACH mode files is the only one which is insisting on adding a unit to X. ... Does that flag setting work only for the Equation Library or is it a more general thing?

No, that flag doesn't have any effect on the generic equation solver. What happened is that your 'x' variable got a unit stored in it previously (probably left over from some other example that you did). Once a variable has a unit stored in it, the equation solver "politely" maintains that unit for you. To make the unwanted unit go away, press ON to exit the solver, purge the variable ('x' PURGE), and re-start the solver.

In general, it is always best to start the solver with non-existent variables, so that their previous contents won't interfere with the process.

-Joe-

[FilmLover451]

> What happened is that your 'x' variable got a unit stored in it previously (probably left over from some other example that you did). Once a variable has a unit stored in it, the equation solver "politely" maintains that unit for you. To make the unwanted unit go away, press ON to exit the solver, purge the variable ('x' PURGE), and re-start the solver.

Thanks Joe! I discovered the problem earlier today and it was as you say: the x variable was hanging about from something I did a week ago which used units. I had assumed (always a bad idea) that variables used in this way would be temporary. In fact, I found x existing as a file in the Home directory with the value 32.5_m. Once I'd deleted it the Solve Equation worked correctly.

I didn't know variables could be purged from the stack screen. That's useful to know. Cheers for the help.

Gill