The AWR 'SEEKER' - Test tool for Astronomers
The Seeker from AWR Technology does a rectangular spiral by driving the Telescope mount through the Autoguider Input and can show mount errors such as backlash, periodic error, stalling, slipping gears, shaft wind up and balance issues.
In astro-photography you can use it as a tool to do mosaics, not missing any part of the sky.
The video shows how to use it with examples of mount errors and a mosaic shot of the moon taken with a small CCD sensor.
For further information look at Test Tools on the AWR Technology web site.