[bilfman]

If you have access to a timing light with a degree wheel on it, you dont even need those marks. All you do is use the dial and keep the line on the "big V" tab or 0 degrees. So for example if you have the engine running and you turn the dial on the light to 12 to the the line on the big v, you are at 12 degrees. These lights are very handy when setting total advance because the stamped tabs only go so high.