The next version of Audio Mastering (2.4) looking very good indeed:
New version of Audio Mastering 2.4 will have visualization tool for more accurate control of Stereo Imaging. Mid-Side vector indicator shows phase difference between stereo channels. Length of vector shows relative volume level.
With this indicator you can measure presence of stereo signal, width of stereo, offset of channels level and possible presence of phase distortion.
Next part it’s spectrum of Side channel. Its bars show presence and relative level of stereo signal on different frequencies. Also this meter shows frequency space for three-band Stereo Imaging module.
Via the Audio Mastering blog.