Testing horsepower and watts from shaft of motor

This photo shows a simple way to see how much horsepower is avalable from the shaft of a motor.
A "prony brake" (inverntors name was Prony) is fastened around shaft and the collar of it is tightened to different tensions to get more or less LB FT pressure measured on a scale.
 
The prony barake arm is usually 1 foot long and so knowing the torque (LB FT pressure) and the simultaneous RPMS of the mtoor, the horsepower can  then be calculated simply with this formula:
 
LB FTpressure on scale  X   RPM of motor / 5250 = HP / 746 = WATTS
Phoito above shows a prony brake with a teflon adjustalbe tension collar and one footl long arm.