
Why Do Calculators Have a Headphone Jack? - bane
https://youtu.be/W_mZ7smIz3U
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simonblack
Its usually the older and cheaper calculators that have a jack.

They're not a 'headphone' jack but a charger for rechargeable batteries or a
battery-replacement source of electricity. Most of the time they are the
narrower 2.5mm rather than a 3.5mm socket. I suppose that way back then, the
headphone-style sockets were cheaper and more readily available than the pin-
and-sleeve charging sockets we use today.

I remember having a simple four-function battery calculator back in the early
1970s that cost $40 then (probably about $350 equivalent today) which had one
of those 2.5mm sockets as a 6volt electricity source.

This was before LED and liquid-crystal displays were cheaply available. So
they used a gas-discharge display which was both expensive and power-hungry. A
set of batteries would only last about six hours.
[http://www.vintagecalculators.com/assets/images/VFD_3.jpg](http://www.vintagecalculators.com/assets/images/VFD_3.jpg)

