My timing belt broke.

The mark on the camshaft sprocket is obvious.
But I can't figure out the corresponding
pointer to set the timing right.

The "pointer" is a plastic thing with three
definite ridges (they show in the observation
hole in the timing belt cover) but
no white mark to explain
where to line up the mark on the sprocket?

I set it to the middle mark & the engine runs,

 

In my post concerning your t-belt installation,I advised that after laying the new belt on,with no slack on the drivers side,and turning the crank twice to make sure that everything lined back up,the cam sprocket pointer should have came back to the middle line! If you were off a notch, the pointer would have been way to the left or right,so you would have obviously known something wasn't right.The fact that it runs and you haven't complained about any power loss or other problems tells me you got it right! Congradulations !
Phillip