This is the seat drawing from Mike Dunbar's book.
Scale measurements added.
My graph paper, at 17 squares, was exactly 3-13/32", and the depth of the seat at 2-19/32" was exactly 13 squares.
So, I made a 17 x 13 square grid on the copy with the scale measurements.
I laid this drawing onto a piece of aluminum flashing and transferred the shape and drilling points. It is important to mark the center line as it will be used for aligning this template correctly on the wood when marking out.
And finally I drilled a small hole where spindles and legs will go. I used a #60 drill bit.