Just completed this sine protractor.

Its simple to use the distance between the centres is 100mm so to set it to desired angle its just the sine of the angle times 100 move the decimal place two jumps to the right.
This is how you set it:-
Zero you digital height gauge on the top of the roller.

For 30 deg the sine is 0.5 so the height to set the roller is 50mm

Then just use it to set your work at the angle

You can obviously work the other way and use it to measure angles.
Stew