Septum Polarizer Ports Identification LH RH ?

Even keeping in mind the multiple definitions of what is Left and Right..
https://en.wikipedia.org/wiki/Circular_polarization
.. and the contradictory stuff in various publications..

A septum polarizer has a square input, with a couple of step changes in dimension, these being for matching.

Then, the key feature is a thin sloping vane, straight up the middle, with a profile making it look like a very narrow
set of stairs. The initially square input becomes progressively divided into two familiar rectangular waveguides.

If a RHCP polarized wave enters the square, and hits the stairs, which side waveguide will the RHCP energy
modes be forced into?

I would love a easy way to tell, and to remember this.