When I made a spiral - when it said 12 inch line I used the number 12 on the ruler. If the next cut was to be 11 and 1/4 I put it on the number 11 and 1/4 on the ruler. The horizontal lines being the used on the bottom of the fabric. It took a bit to get used to using the numbers for measurements
You should be able to find more instructions on the internet. Carol