The upper portion of the loading fixture is affixed securely
and firmly on the table using a second C-clamp and
positioned so that there is a small gap between it and the
optical mouse. The reference surface should be able to move
freely. This can be confirmed by pulling the reference surface
up and down slowly. The gap between reference surface
and optical mouse should also be kept within 1 mm; otherwise
the optical mouse will fail to register any movement.
Once these precautions are adhered to, the weight can be
hung on the fixture. The extension of the polyethylene film
is recorded at fixed time intervals (typically 10 seconds) for a
certain period of time (typically 5 minutes) using the stopwatch.