It's called "slew rate" and its inherent in all ignition boxes. I'm not smart enough to say why one design has a better slew rate than another, but certainly it's quicker electronics. Don't forget...a timing light has a slew rate also. A cheaper light may not be as slow as a dial back. Or it could be.
That's why setting timing to a nominal value may not be what it really wants. The only way to really know what the engine wants is to test and look at the plugs. Always use the same light every time.
