I worked without a spotter. It was me versus the machine. A dance partner whose construction and integrity consisted of materials ranging from paper clips, ball bearings and flags to pianos, oil drums and sledge hammers. All of which were meticulously placed, fashioned and organized with incredible attention paid to detail and the laws of physics. Bump the table -- fail! Kick a trigger -- fail! Stumble on a ramp -- fail! Get caught up in a swinging tea pot hung by fishing line -- fail!
There were an endless number of random variations to account for. I mentioned some of the ones related to temperature and humidity, but they could be totally random. A ping-pong ball bounces too far. A mousetrap snaps unexpectedly. In one case, a cardboard box bounced farther than usual, and triggered an oil drum rolling down a ramp too early.