Prognosticars are especially sensitive to the fluctuations of the Warp, which allows them to detect the psychic tremors that are inherent in daemonic incursions into realspace. Thus, a Prognosticar is capable of determining the location and severity of such an event. This skill appears similar in manner to an oracle in form, though in function it is similar to a highly specialised form of hunting instinct. Within the Chapter Augurium, Prognosticars conduct their rituals and meditations in the light of candles where their divinations forewarn the Grey Knights in their deployments.
This allows the Grey Knights to send their warriors based on the nature of the threat at hand rather than delayed or faulty battlefield intelligence reports. Whilst there is an element of inaccuracy, without the service of the Prognosticars, the duty of the Grey Knights would be impossible to accomplish. Thus, Grey Knight commanders often do their duties out of pragmatism rather than due to callous disregard of life, as they are well aware of the dangers of a daemon due to the divination of the Prognosticars.
The divinations performed by Prognosticars are extremely taxing and result in their body aging at an accelerated rate. Initiates with the potential to become Prognosticars are very rare. For instance, during the First War for Armageddon, only a single Prognosticar, Torcrith, served the order. This may have contributed to the Grey Knights' relatively late realisation of the daemonic incursion.[2a] Several years after the war, Hyperion - who himself had been considered a potential recruit for the Prognosticars but had been discarded because of his lack of focus - became a new Prognosticar. When Torcrith died a few years later Hyperion in turn became the only Prognosticar.[2b]