Figure 1 represents the advance curve obtained on the test bench of the distributor alone (advance in distributor degrees in relation to the speed of rotation in distributor r.p.m.), the point 0° being the point at which the breakers open when the distributor is at rest. On the engine, the spark advance at a given speed the number of crankshaft advance degrees between the moment when the spark occurs (firing point) and the T.D.C. of the piston.