(the correct term is HR Signature or HRS. An HRD Signature is the readout recorded by an HR Device- since an estimated 87.6% of the sentient population require an HRD to perceive an HRS, it was a given that the less accurate TLA would become the most widespread)
Holt/Rischmann Device Signature : Quantitative causality influence, projected strength of will, or active psionic potential* of an individual measured against the local AEI. Modern HRD detection equipment (pioneered from research done on seemingly defective light temperature sensors) is capable of adjusting a sampled signature against the local AEI if the local area has been sampled previously. This allows for an individual who would read as (say) 1.0 in standard AEI to read as 1.0 in an AEI of 0.5. Uncalibrated, the detector would list the individuals potential at 0.5, which is technically incorrect.
An HR Signature is inherently variable, tending lower when depressed, at rest, or ill; tending higher when aroused, angered, excited. An HRS is considered accurate if the HRD is run for a period of five to ten seconds- long enough to pick up the spikes and oscillations of mental disturbance.
The equipment used to measure and compare projected and absorbed energy was developed by quantum physicist Ernst Holt and IX° hermetic Alexander Rischmann in 1904 GM. The paper, titled "The Quantum Sun : Measuring the Potential of the Sentient Mind" can be found in the stacks of any Federal library.
HR Devices are fairly expensive- a handheld, battery powered unit retails through channels for ~9,000$ (in adjusted USD), and larger, "mass" models (such as the types used in schools) and the equipment to run them run in the millions. Area monitors ("HRD radar") of the type used by the Templar and Heirotus run into the tens of millions for ground or otherwise atmospheric installations. Spaceborne hardware has vastly greater range and accuracy, assuming the enclosure is set up properly- being free of magnetic fields, atmosphere, and sentients does wonders for acuity of the hardware. The opposite is also true- HR Devices don't function very well in crowds or areas with a high organic density, such as dense forest or jungle.
Advanced hermetics such as Greymalkin and Grij are experienced enough to be capable of turning raw intuition and instinct into accurate HR data. When Greymalkin mentions that an HR oscillation on Prime registered further up the annex, he isn't necessarily referring to hardware detection... though it certainly helps to have Templar satellite monitoring data to turn "WEIRD POWERFUL ENERGY THING OVER THERE!" into concrete numbers.
* Here differentiated on the grounds that psionic potential is just that- potential, and not necessarily willed. Empaths are the traditional case example- not liking the feel of your supervisor's hangover doesn't change the fact that you can still feel it. A quick sweep with an HRD can calculate just how much potential (read: susceptibility) a psionic talent has at that point in time. Federal public schools use fulltime HRD monitoring to determine what classes students are assigned to, with an eye towards evening out spikes (anger, rage) and drops (depression, guilt, etc.) in the student body.
