H-CAT P-12B Linestage

I bought you a H-CAT preamplifier a few weeks ago for which no manual or instructions were attached. Could somebody tell me the functions of the Wavefront setting. I believe that the adjustment is automatic, but what is the function of the black button on the side of the adjustment wheel?
Thank you in advance for your explanations.
Thank you so much for thinking of me. I'll let you know about the Wavefront settings once I receive the unit.