125hp Force 1985 Timming Question

[14GR8BOATING]

I am adjusting timming on my 1985-125hp Force motor- dual carb.'s because the plastic timming bracket broke(have repaired bracket), and the manual is not very clear on this. I can locate the timming indicator bolted to the block and there are only 2 marks on the flywheel aprox. 3" apart. I am assuming it needs to be in between these 2 marks but where. I have found "TBC" on #1 firing cylinder, have a volt meter and timming light, but what next? In the chart on the book it says 30 I believe. 30 from what, where,.....I live in the Arizona desert and water is kind of far away so I am doing this without motor being in water. Hope this is do-able. Thanks to whomever gives me some tips.