One alternative to floating the scope is called quasi-differential or channel A minus channel B. The signal is acquired by using two vertical channels and subtracting the difference either in the analog domain, or using waveform math in a digital scope. Notice that the scope ground lead is not used in the measurement. This technique overcomes some of the problems with floating the scope. The scope remains safely grounded and the load is not exposed an unbalanced capacitance on either input. However, channel A minus channel B does not work effectively in situations where the signal being measured is smaller than the common mode signal being rejected, such as an upper gate drive measurement or the voltage measured across the current shunt as shown in the example on this slide. In these applications, the user is asking the scope to measure a small difference between two large signals. Small errors in gain accuracy of the one channel relative to the other can be larger than the difference the user is trying to measure.