It looks like an inverted pendulum to me, with a spring hinge at the bottom.

On 10/24/09, meredith lamb  wrote:
> Hi James,
>
> Thanks very much for the E-Bay note on the seismometer!  The pictures were ~
> vague, but I think I see the flat metal strip on top.  Interesting hanging
> mass approach.  I am "speculating" that it has a photo sensor
> on the bottom for rough centering purposes?  The seller may send a PDF
> file on such which might
> also give more overall insight.
>
> Makes me wonder whether a round piano wire that replaces the flat metal
> strip would work out?
>
> Meredith
>
> On Fri, Oct 23, 2009 at 8:14 PM, James Allen  wrote:
>
>>  To Meredith and all, there is a Kinemetrics SH1 currently listed on Ebay
>> with the case removed so that you can see the mechanism.
>> Jim Allen
>>
>>
>>
>>
>
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