Modifying faction in LUA

[Baete2]

I've been trying to track down the right way to increment faction based on a turn in event and I'm missing something so looking for help.

The best I can find is that I should use:
e.other:Faction(faction number, increment amount?,0)

so my quest script has:
if(item_lib.check_turn_in(e.trade, {item1 = mycoolitemnumber})) then
e.self:Say("Some cool mystic quest text");
e.other:Faction(faction number,10,0);

I have no idea what the 3rd number is for and can't find a link with docs anymore they're all dead links.

What I want to do is have the faction increase by 10 for each turn in, but it's not working...it just sets the value to 10 each time. I know it's got to be something simple I'm missing...so any help?