ignition timing trouble!

[2.4niz]

My 92 240 failed emissions horribly yesterday. I can take care of most of it, except the timing. The guy said the timing was set at 25 degrees, and said that it is supposed to be at 20 degrees, and the emission sticker on the car reads 15 degrees, so that confuses me. I checked it for myself and that didn't help. There are 6 lines on the crank pulley, none marked zero or any increment. The pointer shows up to the right PAST the last possible mark so I know its way off, but I have no idea which is 0, 5, 10 degrees etc.

I need to know which mark is which, and what the procedure for timing is ( do I need to unhook anything, if so where is it etc.) thanks for your time!