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Very early exposure
One of my first field service calls ever came in 1967 when a local school was having trouble with the clocks throughout the school. It seemed every morning the clocks were over four hours slow. The system used a controller that sent a pulsed signal through the power to advance the minute hand, coordinating all the clocks to change at the same time. The controller appeared to work fine but each night the time changed. It took me an overnight stay to find the problem. Camped out in a classroom to await any event, around midnight I noticed the clock was advancing the minute hand at a rate of a second hand. A quick survey showed all clocks doing the fast advance. I ran across a janitor buffing the floor near the front office and when he stopped buffing, the clocks stopped advancing. Seemed a bad set of brushes on the motor was inducing spikes into the power line throughout the whole school. After replacing the brushes everything returned to normal and the clocks kept accurate time.