individual ignition trims will be applied at the same time. For example, a -12 degree 4D ignition trim and a +6 degree 5D ignition trim can both be applied to a +20 degree value from Ignition table 1, giving an ignition angle of 14 degrees BTDC. 20+6-12 = 14. If you are uncertain about this open the runtime values window (F12 key) and look at the ignition tab. You can see the value from ignition table 1, the various trims, and the actual ignition angle being used. Scott