It effectively is an ASI combined with an altimeter. The Airspeed indicator readout is corrected using the standard ISA relationships (also,the scale is obviously calibrated in mach!)
The design of the pitot head is also significant, especially for supersonic flight (the flow entering the pitot tube is subsonic as it will have passed through a shock. You do get the corresponding increase in pressure though).
Hope that helps, bit more simple than pressure rise across stators :-)