In this article in the Electronics Weekly test and measurement supplement in June 2013, I describe how the Yokogawa DL850 ScopeCorder is used as a measurement system for real-time calculations of power and efficiency in power electronics devices. Examples include the display of the measurement results of a rotating body in polar coordinates in real time: for example when measuring the wobble of a rotating body, the measurement of transient power and the measurement of the electrical angle of motors.