James,

I ran a Sprengnether vertical at the USGS in Golden some years 
back.  There was a small weight on the boom and a means of moving it 
back and forth (without removing the cover) to adjust the zero 
position of the sensor.  From time to time the spring would sag a bit 
and the weight had to be moved toward the pivot.

Cheers,
John Lahr
Corvallis, OR

I'm about to leave town for a while, so one of the systems I'm 
running is certain to have a problem soon.  They look OK so far 
tonight, though:
http://jclahr.com/science/psn/chor/#


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