a method and device for monitoring and measuring underwater physical therapy or exercise employing fluid elements in either enclosed compressible fluid filled chambers or aquatic exercise devices submerged in water . measurements are taken via pressure ports formed on first and second opposite surfaces of the hydrodynamic device to provide a pressure differential signal . this pressure differential signal may be compared to a calibrated zero signal to form a measurement signal . the measurement signal is then converted to a digital signal for evaluation by a digital computer . the exercise performed may be stored and evaluated . the arrangement provides information with regard to the type of exercise performed and the degree of exercise performed .