Bill is correct, the missing tooth is much ahead of TDC, there is much to, things like dwell for spark. It is often placed where the gap it is not encountered in timing measurements. The first rise after the missing tooth is the sync.
As a side note.
The way the gap is sensed if fairly simple. Teeth are measured using a timer registers, if the span between teeth is greater than 2x, it is the missing tooth, the actual time is 3x. It is easy to do with micro, only a subtraction, bit shift and compare, very fast. The subtraction needs to be done anyway, because it is used to measure the interval that is later subdivided for timing resolution . Since a normal tooth is 1x, the 2x test works and rejects any false triggers, because the engine cannot change speed fast enough to make it fail.
