I believe the scan-gauge is simply providing the information given to it by the ECM on the engine. I have a CAT TECH program that was used for data reading by technicians on the cat engines. It does provide a computed HP reading. I don't think that it is accurate at all but does provide some number for a base line to measure decrease or increase in performance. The numbers on the scan-gauge appear to be the same that shows on the CAT TECH so it is not a scan-gauge computed number but rather from the ECM. I think you can adjust the reading on the scan-gauge to more accurately reflect the real HP output of the engine.