Derek Cohen (in Perth, Australia)
Hi Don

You can see that I am using a sliding bevel in this picture ...

I made four angles choices: 1:5; 1:6; 1:7; 1:8

Each of these is a ratio, for example, 1” across and 7” down.

On a piece of paper/MDF/ply, scale off 8” in one inch increments along a verticle axis, and a single 1” mark along the horizontal.

Now use the sliding bevel to connect the 1” to whichever ratio you intend to make. That creates the angle you see in the photo.

Regards from Perth

Derek