In our shop, we are often given "opportunities", which best translates as the big boss asking you to make a sample. I found this cute place mat in the book Log Cabin Quilts.
When I started gathering supplies, I felt guilty opening the package for the ruler. It is honestly a little pricey for making one place mat. Once I opened it, though, and started following the directions in the book, & felt the grippy spots on the back, I ended up buying the ruler myself.
Each of the darker squares sits on the center square, and you trim the excess off leaving even edges for each row of the Log Cabin. The grips on the back keep the ruler exactly where you set it. There is very little measuring once you cut the center square.
The ruler has a QR Code printed directly on the ruler, linking you to a video tutorial which you can consult time and again.