Origami, also try marking your ruler with some tape. I have the 1/4" seam line masking tape but blue tape can work too. I wish I could show the rulers I've adapted for this project but it gives away size into and things I shouldn't say.
Earlier in this thread though showed a ruler I used on a different project and the diagonal tape line I placed so I could trim 7.5" QST blocks. Same concept but smaller sizes here.
Bonnie Hunter's 2019-2020 Frolic Mystery