"mike" wroteWhy not put the rods on precision
bearings, under glass, and roll the
device at a constant speed on level rails over areas of question?

Otherwise, you're measuring human frailty, wind direction, incline, or
acceleration. I don't know what people think they'd be measuring...
it can't be magnetic fields, or they'd use a compass.

reply:

http://simmonsscientificproducts.com/products.html

Something like this?