Its just a rotational strain gauge and a digital encoder wheel. It measures torque with the strain gauge and converts it to HP. I built one of these for a design project using labview and an industrial rotational strain gauge used on fracking pumps. Total cost was around $150. The head of the ME department wanted to use it for an engine dyno for the thermodynamics class here at UD. I designed and CNC'd a flange to go on their 350 crate motor we had set up in a jig already. Designed and programmed the controls for the engine as well as had sensors (coolant temp, RPM, EGT in every runner, and also a mass air meter as well as a flow meter for the fuel [to calculate BSFC to calculate HP and compare]). After all the work was completed at the end of my freshman year, the engine dyno was ready to operate, worked all summer, came back to school to find they had torn down the ME building and scrapped the dyno. Son's of bitches!