Understand device was a gondar divination spell that allowed a cleric to completely learn and fully comprehend how a specific device functioned. The specifications of its casting were found in the "tome" known as The Argyr.
When cast, this spell imparted complete understanding regarding a chose device. Its specifics of its creation, purpose, functionality, how it was to be maintained along with all of its components, including requisite substances, fuels and even spells became known to the caster. They became aware of any activation words and actions required in its operation, although skill of use was still improved via actual practice.
A machine or device did not need to be in complete functioning order for the effects of understand device to occur. In fact, the affected object could be partially destroyed or even shrouded by magical means.
In addition to verbal and somatic components, understand device required the use of a glass rod that had been blown into the shape of Gond's holy symbol, which was consumed during the spell's casting. A cleric's personal holy symbol could be used as a replacement material component, even if it was crafted from a different material, however it was similarly destroyed.