Sorry, I read your post earlier and went looking for a pic but got sidetracked...I do believe the marks are 2* each since they are marked at 10 and 20 and there seems to be half as many marks...I will see if I can find a shot of one for you, but you can also search using the toolbar at the top.
Search for 2.3 timing...I know there was one in my Haynes manual...let me have a look...yes...on page 2A-3 there is a diagram, actually...the bottom number is 10* ATC and it goes by 2's to 0 (so five marks) and then it goes all the way to 30* BTC also by 2 degree increments...
So if you can see any marks the ones closes to the engine are 30* BTC...the one at the bottom right (looking down at the marks) would be 10* ATC...
Hope that helps...