HP-21 fast counter

[TKuenzi]

Hello,


My first calculator was the Hewlett Packard HP-21

The calculator is not programmable. But I was able to display a fast counter:
-direction up / down not under my control
-10 digits counting capacity
-the units are counted in binary and displayed in hexadecimal mode
-the characters are 0…9 – E H o P r
-the speed of counting was between 100 … 1000 units per second.

To start a counter:
1. Plug in the battery charger
2. Slide the On-Off switch *slowly* to on.
3. If 0.00 is displayed, switch off and repeat step 2.
4. If a counter is running, you are done!

Has anyone else noticed this counter?

Kind regards,
Thomas

[J-F Garnier]

Same as here ?

J-F

[Maximilian Hohmann]

Hello!

I remember this from my school days. None of us could afford a calculator from HP, but you could do a similar thing with some Texas Instruments models that come with a clip-in all-in-one battery pack, eg. SR-50, SR-51 (both of them excellent and rather underestimated calculators!) or the Ti-58/59 series: Loosen the battery pack and place the calculator on the desk so that it sits on top of the battery. Turn it on and tap lightly on the table so that the battery loses it's connection momentarily. In some cases you will just get a screen full of hieroglyphs, but often the calculator will start counting at high speed!

Regards
Max

[John Garza (3665)]

I seem to recall something similar published decades ago in the PPC Journal. Something like removing the battery door (but not the battery) of an HP classic machine and tossing it on a bed. Supposedly, just the right toss would yield just the right power glitch to see strange displays, access block 3 on a 67, etc.

-J