* This mark is located on the crankshaft pulley.
* It indicates when the piston in cylinder number one is at the highest point of its travel.
2. 6 Degrees Before Top Dead Center (6° BTDC)
* This mark is located 6 degrees clockwise from the TDC mark.
* It is used when setting the ignition timing.
3. 10 Degrees After Top Dead Center (10° ATDC)
* This mark is located 10 degrees counterclockwise from the TDC mark.
* It is used when setting the dwell angle on points-type distributors.
4. 30 Degrees Before Top Dead Center (30° BTDC)
* This mark is located 30 degrees clockwise from the TDC mark.
* It is used when setting the timing on some Ford engines with electronic ignition.
