Did a little front end engine cleaning to day, even after cleaning it's har to say, but to me it look very much like the pointer sits right on top of the belt pulley. Even with a light it difficult to see.
Anyway, with the distributor clamp just loose ajust idle as slowly as possible without engine stalling and turn it a little forwards or backwards until the engine speed is highest. If the engine then pings retard timing a lilltel (or use 98 octane RON).
If it still pings your advance mecanism is faulty and need fixing (cleaning, oiling or new springs).