Please see the source code for details. The data loss is tolerable however. This is an intolerable error and must cause concern for all data taken around transit in the last month. A repeat of this run with the empirical correction disabled will be requested tonight. The theory holds that the amplitude of the hysteresis should be proportional to the imbalance.
Elevation encoder collar slippage - the encoder is connected via a collar to the elevation axis.
The bolt connections need only allow one micron of slop to produce the amplitude effect seen in these tracking data. The second requires a tightening of bolts, some of which are inaccessible without complete removal, and replacement, of the encoder. In each case the acid test is repeating the tracking experiment. This behaviour may need addressing, but it is beyond the scope of the current issue. The necessity for action could not be clearer, and it is fortunate perhaps that we had planned, yesterday, to take immediate remedial action.