[question] formula for final weapon damage stats?

[sublogic]

Need help from those who may know.

So far, I know that a final weapon instance, defined by (weapon, maker, model), has stats influenced by
1. weapon (e.g. katana)
2. maker (e.g. homemade)
3. maker-model, (e.g. homemade-rusty blade) which gives a mod level value?? specific to the maker-model pair.

(values are read using the provided mod tool: forgotten construction set)

But I have no idea how the final stats are derived.
In particular, I do not know the influence of point 3 from above. (the mod level is just a value like 15 for "homemade rusted blade". the mod tool tip says add/sub, which I can't figure out).

And other than the above, are there any other influences?

Basically, I am trying to see whether a clear formula can be established between the factors and the final stats, to investigate whether the stats of weapons in the wiki can be dynamically computed from the base definitions, instead of requiring manual entry.

thanks in advance.