Hi Bryan,

The period is measured over one complete swing, from left to right and back 
again.  It's not easy
to get a period greater than about 15 seconds.  If the connection between 
the mast and the base
has the least amount of flex, then the mast will bend very slightly toward 
the boom.  The symptom
of this is that the boom will tend to swing to one side or the other rather 
than finding a stable
center position when the period is adjusted to be very long.

Cheers,
John


At 06:21 PM 4/1/2005, you wrote:
>I have built a Lehmann seismorraph using the 1/2 pipe and using the pipe 
>union for a pivot point.
>My question is when setting the period for the 30 inch boom.Is that from 
>left to right then back to left if this is the case I am only getting to 
>about 10 sec also should the boom be level. Should the gate effect take 
>care of the swing back to center.
>
>It has been about 4 years since I built the last one and I dont remember 
>having so much truble setting it
>thanks Bryan S Goss


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