Timing Marks 64 283?

[Texasdeere]

I figured out my intermittent miss was too much ignition timing. I did retard it some but I don't know where it is supposed to be set. There is a "0" and an "A" on the tab with hash marks. I assume the hash marks are 2 degree increments? I have it set around 10 degrees now (I think) but I need to bring it down a little more.

Can anyone tell me where the factory ignition timing is supposed to be set?

Thanks