I wanted a larger center, so it is cut 3 1/2" square.
The ruler is designed so the only markings are what you need to cut each "log" for your quilt.
I began with size "c" and cut enough "logs" to have three lights and three darks on each block.
Here are the first two finished blocks. This will be my "leaders and enders" project for the foreseeable future.
My blocks are 9 1/2" raw edge-to-raw edge. That means I will need at least 100 blocks for a bed-sized quilt. Maybe I should add a couple more logs to each block!