Ian,

If you are just wanting to measure tilt (rotational oscillation), as 
Randall Peters has pointed out elsewhere, the natural period doesn't enter 
into the calculation.  Natural period does get involved with a second-order 
effect related to moments generated by an imperfect hinge or by intentional 
damping, but those could likely be reducedd or ignored.  I think, In 
general, for measuring rotational motion you would prefer a pendulum which 
maintains a stable position rather than a less stable long-period setup.

Brett

At 01:33 PM 2/25/2008 +0000, you wrote:
>Hi,
>
>I didn't get very far, due to lack of time.  I used a threaded rod which 
>screws through a threaded hole in the body of the pivot.  The rod was only 
>5mm in diameter and wasn't very strong, so when the pendulum was heading 
>towards each extreme it would bend and the pendulum's motion was very 
>complicated.  My next step would be to try it with a larger diameter rod, 
>one day...
>
>With the limitations mentioned above, I only got 5 seconds out of it and 
>it wasn't stable enough to behave in the way it should, like resting at 2 
>o'clock.  I think the main benefit of an asymmetrical arrangement will be 
>that you get more movement at the bottom end (for a given length) which 
>may make seismic excitations of the pendulum (as a tiltmeter) measurable!
>
>Good luck!
>
>Ian


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