Question about base skill level and modified skill level.

[Lascivious Goat]

When does modified skill level come into use versus base skill level. I know that base skill level is used to determine when a character can begin to take up a certain profession (e.g. base Tanning skill of 150 required to become a Weaver) or that a tiered weapon can't be used until a character has reached a base skill in the appropriate class of weapon. In what situations is a character's Modified skill level used?

[Tantalyr]

Besides the two you mentioned, base skill is also utilized when determining whether you can scribe a spell (not the formula, but the spell itself). As far as I know, in all other circumstances your modified skill controls (e.g., scribing formula, using tools, etc.).