Variability in the escape wheel of a Seth Thomas #2

The graph below shows the performance of a Seth Thomas #2. This escape wheel does not appear to be eccentric — the rate is relatively flat. But there are large differences between the teeth. The variability of rate with each rotation of this escape wheel is 1.9 hours per day. You can clearly see the repeating pattern of tooth spacing in this graph, which shows about four complete rotations.

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