Method and apparatus for displaying measures of distortion present at the outputs of a quadrature demodulator. From each of the in-phase and quadrature channels of the demodulator there are acquired n parallel bits, m of these bits being the demodulator data output of the associated channel and (n-m) bits being error bits for the channel. The n bits for each channel are converted to a signal acceptable to a plot display device and applied to orthogonal axes of the device. In addition, an absolute value of the (n-m) error bits for each channel is derived. This absolute value is filtered and displayed, as by a meter, for each channel.