Semantics....Almost ALL ignitions are auto advance...The difference is at the beginning...C&H, RC EXL, and some others are statictimed at 28 or 30 BTDC..DA, Falkon, and some others are timed at about 2 BTDC....When starting with an engine timed at 28 the first 1 or 2 flips retard the ignition to about 4, from then on its AUTO advance until around 4000 rpm...It stays there until the rpm drops below 4000, the ignition RETARDS with rpm and will ADVANCE automatically until 4000 again...
The ignitions timed at 2 BTDC start there and ADVANCE until whatever they're made to do, probably at about 4000 like the others...They will RETARD when rpm drops below the high advance point, and automatically ADVANCE again when rpm picks up...
Years ago we didn't have the auto advance option, so some ignitions were mechanically linked to the carb shaft and ADVANCED with throttle opening...These reached full advance at WOT, not the lower rpm that today's EI ignitions do...
A Hall sensor will react only to one magnetic pole...MOST are set up to use the South pole to react to the Hall sensor with the part number on it...It can be set up to use the North pole if the sensor is turned over to the blank side, so an ignition with two magnets is using the South pole of one and the North pole of the other for some other function...
Early Reichmuth ignitions had 2 magnets...The advance function changed from the starting setting to the higher speed setting at around 1500 or 2000 rpm without a ramp, so there was an abrupt timing change, resulting in a big change in rpm just when the engine was coming down to the rpm wanted for landing...He later changed that to a more linear system, but doesn't seem to be around anymore...
There was another ignition that had a small pot to adjust for max rpm, he doesn't seem to be around anymore either...
Al Deim called his ignition Silent Spark...Worked well, he doesn't do much anymore either..They worked well, I bought lots of his capacitors when making my own fixed ignition...Ed Vollmer came out with the automatic advance part of ignition many years ago..First used by C&H, it worked very well when used in series with a fixed ignition...
Not all Chinese ignitions work well...The RC EXL is the very best...
There are a few other ignitions made and sold, but probably 98% of all manufacturers use a version of C&H and RC EXL....There is no better ignition system made....
Equal maybe, not better, just more functions...I myself like the K I S S principle, 4.8 volts..There is no SANE reason to use multiple batteries and regulators when a little 800 MA 4.8V 2 ounce battery will run a good igniton for at least 2 hours...Unless you just GOTTA follow the high tech crowd....Simple is BEST..[8D]
ALL EI systems use crankshft rpm to work...If the crank rpm doesn't advance, the igniton doesn't either...Electronics don't have ESP, they can't predict where the rpm is going...If the low speed needle is set too rich the rpm won't change very fast when the throttle is advanced, so the igniton timing lags slightly...The difference is infinitesimal, but a mechanical advance is actually faster at reacting than an electronic advance..Electronic advance follows the throttle EXACTLY, EI follows crank rpm..The tail is wagging the dog...