> I've seen these things on quite a bit of older equipment, "Time
> totalizers" consisting of a glass tube filled with a murcury bubble that
> moves maybe an inch over 5000 hours. For instance the one at the bottom
> of this page:
>
> http://www.surplussales.com/Meters/MtrTime.html
>
> I'm curious, do they still make them? How do they work anyway?
>

I'd be surprised if anyone makes them anymore, ROHS compliance would
be an issue.

They work by electroplating the mercury across the bubble. You feed
them a small constant current.
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