If encoders are used, when tracking is off, if you grab the
scope and move it by hand, the changing encoder values will update
the current altitude and azimuth. When tracking is on, if the
encoders differ from current altitude and azimuth, the situation is
understood to be one of slippage of the drive shafts, or perhaps a
wind gust moving the scope off position. The scope will slew back to
the proper position and resume tracking. Do not intentionally move
the scope by hand when tracking is on if the encoders are on. To
illustrate this, the following is an incident that happened at a
recent star party.
Greg Granville writes, "The 12.5" scope is working very nicely with this setup. I recently added encoders to the scope. At a star party a few weeks ago, a youngster was up on a ladder a few steps looking at NGC 4565. When coming down the ladder, he accidently pushed the scope and caused it to slip on azimuth. He seemed a bit surprised when the scope responded by automatically moving back to the proper position!"
The variables EncoderErrorThresholdDeg and TrackEncoderErrorThresholdDeg control the allowable difference between scope and encoder coordinates before a reset to encoder coordinates occurs. There are two variables since a tighter tolerance during slewing to a target position is often desired compared to the tracking reset tolerance. Set these to a value that represents at least one if not two or more encoder counts. At any time the scope can be reset to encoder coordinates via the 'reset to encoder menu option'. When a reset to encoder coordinates occur, if you wish encoder these threshold violations to be recorded, set the config.dat variable MakeEncoderResetLogFile to 1.