Abstract: An inverted pendulum seismometer mechanism has a massive boom (20) mounted in friction free crossed leaf spring pivot bearings (24) clamped in V grooves 28 on a frame (10). To lock the boom for transport, without straining the bearings, a camshaft (70) turns and, sequentially, cams (72) lift pivot clamping levers (30), guide webs (80) embrace the boom, and a cam (74) lifts the boom off the V grooves until probes (56) on adjustable locking screws (54) in the frame top cross beam (14) engage recesses (58) in the top end of the boom. Further rotation of the camshaft reverses the sequence to reconnect the boom to the frame in an operative state.