How an ignition works

The ignition distributor is an important part of the engine. The ignition controls the timing and charging time of the ignition coil. Besides, it diverts the high voltage spark from the coil to the correct cylinder spark plug. It directs the high-voltage spark from the ignition coil to the appropriate cylinder spark plug. The spark ignites the fuel in that cylinder, creating a small explosion in the cylinder. This energy makes the cylinder move. Without the ignition, fuel would not get ignited and therefore, the engine would not move.

The ignition coil is a transformer and consists of a primary and a secondary coil.
When applying a voltage to the coil, the current flow starts at zero and ramps up. During the current flow, energy is stored in the coil in the form of magnetic energy. The longer the inductor is on, the more energy is stored. This energy is later on needed to create the spark. A good functioning coil is important for a smooth running engine.

Your original distributor does the making and breaking of the coil current, with contact points. These contact points need regular maintenance, such as adjusting the spacing between them and removing oxidation. A capacitor over the contact points prevents constant sparking between them. These sparks would otherwise damage the contact points.
The mechanical distributor also contains many mechanical parts, including springs. The centrifugal force that occurs during rotation causes these parts to move. The parts change the timing. So the timing is set based on the engine speed, causing centrifugal advance.

Combustion of fuel takes time. The spark ignites the molecules immediately around it. These molecules ignite the molecules next to them, etc. If you captured this on slow motion video, you would see a flame front from the spark expanding rapidly. Because combustion takes time, the spark must ignite the fuel at a certain point before the cylinder reaches top dead center. The faster the engine goes, the earlier the spark (in degrees). The better the timing curve, the more efficient the engine will run and the more performance you will get. This timing of the spark based on engine speed is called centrifugal advance. The name is based on how rev advance works in a classic mechanical distributor.

Some engines also have vacuum advance. Vacuum advance does not provide additional performance, but only serves to improve fuel efficiency.
An additional component on the housing, the vacuum pot, provides this. The vacuum pot contains a diaphragm. When vacuum is applied, the diaphragm moves to one side and mechanically pulls on the distributor to change the timing. It should be noted that in many cases, wear and tear on these advance parts often causes the centrifugal timing to be off, or even not work because the parts are stuck.
An example of vacuum advance in practice. You are driving downhill from an incline, if you want your speed to remain constant you will have to throttle down. In this case the engine gets a lean fuel mixture, a lean fuel mixture needs more time to ignite properly in your cylinder. With vacuum advance you make sure you spark earlier, so you give the mixture more time to ignite.

Unlike a mechanical ignition distributor, the 123ignition controls everything electronically. All mechanical parts such as contact points, centrifugal weights, springs and vacuum canister are replaced by only one part: the 123-circuit board. The internal electronics take care of the correct advance and optimal contact angle at different speeds. A vacuum sensor replaces the whole vacuum canister. This vacuum sensor measures and controls the vacuum advance.

The 123igntion is broadly available in 3 variants : 123\Switch (16 for programmed curves), 123\Tune (PC interface via USB) and the 123\Tune+ (Bluetooth connection with 123\Tune+ app).
If you want to read more about the differences between the 3 variants, check out the side-by-side comparison.