First orientate the ECTM graphs such that the Mach line is vertical (this is the constant parameter). Secondly, as it is CAS that you are interested in, place your pencil point at the top of the CAS line and move the pencil down the line (i.e. descending) - as you bring your pencil down the line it will also be gradually moving to the right). Any movement to the right is an increase in value!