Russian joke aside, make your own algorithm.

Write up code to set up your sub to go X speed for Y amount of seconds. X speed meaning a set number for the duty cycle controlling the prop. Make sure Y is long enough for speed to stabilize then save the PSI measurement. Increase X a couple of times, each time saving psi data. You will make your own plot based on your data. It might not be exact according to their 'top secret' calculation method but you shouldn't care. Its all relative. You measure then associate a number with the PSI settings.

If you want to be trick, make your own speed trap using another Microchip and a couple of sensors to make your own algorithm. That might be a bit overkill.