Across my travels I've come across 2 business ledgers. I can't remember where the first one was (I think it was some sort of shop or a jarl's room), I found the second one in the stable house.
Both of them had the following tooltip when moused over "Forge Numbers Business Ledger". Both times I attempted to use them a message popped up "There's nothing to change in the ledger".
What do I have to do to be able to use it, and what does it do when I do use it?
Best Answer
Once you officially join the Thieves' Guild, you'll be able to pick up additional jobs from Devin Mallory and Vex: they'll assign you one of seven types of random quests for you to do.
One of the quests, The Numbers Job, will task you with forging/modifying a random business ledger throughout the world. That's what you need them for.
Outside of that, they're not used.