Tradeskills: question about minimum skill level to attempt a combine

[Minerios]

Heya everybody,

Just wondering how the minimum skill level required to attempt a combine is determined. Is it a set number of skill points below the trivial (i.e. you have to be at most 20 skill points from the trivial level of the combine to attempt it), is it % based (i.e. your skill has to be at least 75% of the trivial level to try the combine) or is it determined on a reciper-per-recipe basis?

Thanks!

 

[Strylok]

I think its something like 25-27 points below trivial....give or take a point.
Also seems the fail rate is pretty high past 10 points from trivial.