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Telescope drives off object when autoguider loop closed

This is probably because the guide errors generated by the autoguider are being applied in the wrong sense, due to the assumed orientation of the guide probe being wrong. Check the following:

• Has the correct guide probe been selected using the TCS AGSELECT command ?

• Is there a possible error with the positioning of the derotation optics ? Check that the absolute and incremental encoders are reading the same value on the TCS encoders page. Check that with the slit angle set to zero, using the handset to move an object in the Y direction moves it along the slit. See Section 32 for more details.

• Could the orientation of the guide fibre itself have been disturbed ? Unlikely, but see Section 33 for more details.