Figure 2: Measured results on the laboratory bell, showing in each case the outputs of the bell accelerometer (upper trace), clapper accelerometer (middle trace), and contact detector (lower trace). Vertical scale is arbitrary, and traces are vertically separated for clarity. For the contact signal, the lower level denotes “in contact” and the higher level “out of contact.” (a) Typical handstroke; (b) typical backstroke; (c) result of a single impact during ringing down.