None = no guilding
Mount = guilding images are sent from the guide camera to the computer running the Guide module / PHD2. Guide / PHD2 works out pulses to move the mount to keep the guide star(s) in the correct position and sends from the computer directly to the mount. So there needs to be a connection from the computer running guiding to the mount. This is usually called pulse guiding.
Camera = guilding images are sent from the guide camera to the computer running the Guide module / PHD2. Guide / PHD2 works out pulses to move the mount to keep the guide star(s) in the correct position and sends from the computer back to the guide camera. The Guide camera sends the pulses to the mount so there needs to be a connection from the Guide camera to the mount. This is called ST4 guiding.

ST4 was the original way to do guiding. Pulse guiding is now the usual way as it involves 1 less connection (guide cam to mount) and 1 less hop for the guide pulses to have to make.

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