From the Flux website:
“Stereo Tool features ultra precise controls of input gain and individual pan for left and right channels. A phase inverter is available for each channel. A global stereo pan and a stereo width settings are also implemented to complete the management of the stereo signal.
Stereo Tool also offers an accurate visual feedback reflecting the signal content. A vector scope display, PPM meters for both inputs and outputs, and a phase correlation meter permanently monitor the signal. “