>> Andy from PHD says that it is a delayed reaction from the DEC axis then overcorrecting.
Matt, sorry for the apparent misunderstanding but I did not say that! Based on what you showed me I don't even think you can definitively say the guiding problem is caused by the mount until you run some experiments to rule out various things, like for example a problem with the camera driver buffering frames. I have seen cases where a faulty camera driver buffered data and that resulted in oscillation in guiding.
