MWO gives the power output for only the motor whereas UWO gives the power output of the total drill system. UWO takes the transmission, clutch, and chuck into account. A drill that has MWO of 600 may only have a UWO of 500. This is a 17% loss in power due to an inefficient transfer of power from the motor through the transmission, clutch, and chuck. If a drill has a MWO of 600 and the UWO of 560, there is only a 7% loss of power. Measuring the drills power at the chuck is more indicative of the drills performance. The drill’s UWO is what the user experiences on the jobsite.