when I set mine, I used a timing light and vacuum gauge to check in 500 rpm increments. I locked my throttle at each increment and adjusted timing for highest rpm at that throttle position and confirmed with vacuum readings. of course this meant my baseline was now an rpm at or above the 500 rpm increment but non the less gave me a target advance curve to match. I prefer to ignore the advance at idle and set the 3000 rpm advance dead on, then work backwards to get closer at other rpm's. idle can be a few degrees off for easy starting and I could care less if off idle is fairly close and w.o.t. is dead on.
