For that I just remember the letters 'ERTM' in order.

They refer to the order that the graph lines appear i.e. EAS, RAS/CAS, TAS, MACH.

When the question tells you which one is constant, that is a straight line up the page, anything to the left leans left and anything to the right leans right.

eg lets take constant CAS:

CAS straight up the page. EAS is to the left of CAS and so leans left. TAS and MACH lean right.

If you are climbing, start at the bottom by the X axis and see which way the line goes. If it’s off to the right, its increasing & if it’s to the left its decreasing.

Descending you start at the top and do the same.

All you need to remember is ERTM for all cases