Depends on the distributor. There should be some letters on the side that show which one it is.
ST: 5 to 7 degrees BTDC (9mm to 11mm before TDC mark)
R252: 1 degree BTDC to 1 degree ATDC (1.8mm either side of TDC mark).
R284: 5 to 7 degrees BTDC (9mm to 11mm before TDC mark)
Glossery - BTDC = before top dead centre. A = after.
Do you have a Haynes manual? They are worthwhile. About £25 from Haynes or dead cheap from eBay.