Hi Kay,

The problem with a fixed pin at one end is that to change to level in 
the long direction, both of the other screws would need to be 
turned.  This would probably mess up the tilt in the short direction.

With three screws, the short-direction tilt and the long-direction 
tilt can be adjusted independently.

Cheers,
John

At 12:22 PM 4/2/2008, you wrote:
>Folks,
>
>A quick question regarding the leveling screws for a vertical seismosmeter...
>
>If you look at the three leveling screws on the AS-1 seismometer at 
>http://www.amateurseismologist.com/, 
>you see that there are two screws on the end with the vertical 
>support and one screw on the end near the coil.  It is obvious why 
>only three screws are used.  But is their a reason for putting the 
>single screw near the coil and not near the vertical support.  Also, 
>wouldn't there be greater stability if the single screw was actually 
>a fixed pin, leaving the other two to be adjustable screws?
>
>Just wondering before I drill the base in my next vertical seismometer.
>
>Thanks,
>Kay Wyatt
>
>


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