When the absolute encoder bulbs are functioning normally, absolute zerosets can be done for all axes:

• USER> ZEROSET ROT ABS
• USER> ZEROSET ALT ABS
• USER> ZEROSET AZ ABS

This is supposed to happen automatically on startup of the TCS, but it's good practice to do it like this at the start of every night anyway.

The absolute zeroset of ALT of AZ will go wrong if an encoder bulb is broken, and the zeroset must be done using a target instead. This can be done for ALT or AZ or both.

To zeroset on the targets switch to computer control first:

• USER> AZ 298
• USER> ALT 89.5
• USER> ENG
• USER> ZERO AZ TAR (if the AZ encoder bulb is faulty)
• USER> ZERO ALT TAR (if the ALT encoder bulb is faulty)

Drive AZ and/or ALT slowly in + direction over the zeroset target points, then switch to computer control again.

When no other method of zerosetting is possible, it can be done using a known position. This requires 2 people, one at the TCS and one under the telescope!