ON THE HP 95LX
This is no problem on the 95LX. Whenever you quit HP CALC on the 95LX and start it back up, you start in the Calculator Arithmetic screen. In fact, you cannot configure the 95LX to come up in any other HP CALC application (TVM, Currency, etc.).
ON THE HP 100LX
You can configure HP CALC to come up in a particular application on the 100LX. In HP CALC press (MENU) Options Startup Application..., and the following screen is displayed:
Set Startup Application in HP Calc: Graphic
Highlight Arithmetic and press (F10) (OK). Set up this way, whenever you quit HP CALC and then go back to it, the Arithmetic function automatically comes up. Of course, you could have selected Currency or TVM to automatically come up.
Rich Hall Editor, The HP Palmtop Paper