Hewlett Packard HP-21 Calculator - Improvements On Hindsight

In restrospect, the HP-21 has been designed with a lot of attention to quality especially so in the functionality of the calculator, but more design effort in the following areas would make the calculator survive the odds of a battery leakage.

1. Improve battery compartment that is battery leak proof.

2. Sealing the LED display from the environment by sealing the gap between the magnifying lens and the printed circuit board.

3. 100% sealing of the keypad against dust/spillage etc.

The reasons that these are not done is probably the fact that though these ideas sound simple enough on paper, implementation in a manufacturing enviroment can be costly in terms of materials, time and eventually money. Weighed against the need for a affordable calculator with good funtionality and a battle harden calculator, it is understandable why this is not done.

However, for collectors it is still not too late to battle harden their HP-21.

The LED display can be sealed with instant glue ( just be careful not to allow the glue to slip into the LED IC chips.

Lining the battery compartment with absorbent paper could prevent damage from leaking batteries ( that is if you still want to use a NiCd ) else switch to more modern leak-proof battery.

Not much can be done about the keypad, as the use of heat stakes to fastened the faceplate to the printed circuit keypad wiring make this a more skill instensive activity.