I'll use MissingTeeth as an example.
In the MissingTeeth decoder the centre of the first tooth to come past is considered zero degrees. If when you setup the wheel that first tooth isn't at TDC then you'll need an offset. But how to figure out what it is? With FreeEMS to make the timing more advanced you increase the offset and to make it more retarded you decrease it. The offset must be less than the decoder total angle (360 for a crank mounted missing tooth setup), you will get no outputs if it is larger.
If the position that you know is really zero is 60 degrees away from the position of the first tooth post the gap, then your offset is one of two values:
- 300 (360 - 60)
Make the offset number larger to advance the base timing, make it smaller to retard the base timing. For example, if you have 10* BTDC in your table, flat, and a timing light shows 5btdc on the engine, then increase this number by 5 degrees. The same applies statically, except you have to think more.