The Sigma series training unit was a model of droid that was employed by Sith Empire at a Sith academy on the planet Odacer-Faustin during the era of the Cold War. The droids had eight arms and bare-bones bodies that were covered in belt-treads, and they were used as targets for rookie Sith students to practice their lightsaber technique on. The droids lacked any significant degree of intelligence and they were not fitted with vocabulators. Following an outbreak of a deadly disease within the academy in 3645 BBY, the students Kindra, Hartwig and Mnah Ra'at found a Sigma series unit wandering through the academy grounds, and they viewed holographic footage that the droid had recorded on its visual mapping system of zombie Sith students that had became infected with the disease.