A dimensional “variance” in the firmament, between Am and Prime and between the Veil and pocket universes, best defined as the relative ease with which Will can be exercised as a Force in a given area. In practical terms, the AEI determines the relative effort required for a Navigator to transition themselves and additional matter into Am, the mental fatigue incurred by a learned individual crossing between realities, and the relative “ease” with which psionic disciplines such as telepathy and remote viewing can be verifiably conducted.

A measurable divergence (positive or negative) from the local AEI is known as a Holt-Rischmann Variance.

While values lower than 1.0 can “feel” negative to individuals accustomed to an environment of 1.0 or higher, unless unduly influenced by an extremely powerful negative HRV the local AEI is always a positive number. 1.0 (+/- 0.1%) is the accepted baseline, as most of inhabited space falls in or near this value. Broad-area variances as high as 3.8 and as low as 0.0001 have been recorded. Verified excessive or minimal variances larger than 300 light minutes are marked on ICG charts as Oases or Sinkholes. While the AEI of an Oasis must be verified to be included in ICG charts, approximated values of Sinkholes are allowed, as an AEI lower than 0.5 is considered to be a Hazard To Navigation.

Fluctuations in the strength and position of Oases and Sinkholes over the centuries have lead to the popular notion of AEI variances as “ethereal weather.”