Sort of an advanced mathematics skill; you get a new tool (an abacus), and with this tool in your inventory, you're now able to make items in larger quantities at a time, perhaps twice or three times as much (or more?). As I am higher level and have a lot more energy, it would be nice to have the ability to make more than, say, 5 white gas at a time.
Perhaps the abacus could be built through a quest, where you have to acquire the pieces? The counting bits maybe being different types of tree bean (so they're diff colors), the frame being "the first harvest from a fully grown wood tree, so it's highest quality wood" or something. Give them a limited lifespan so they need to be replaced or repaired.