"I'm happy for you to indulge yourself," said Harry, blissfully unaware of Hermione's minor flight of temporary insanity. "The vault has a built-in magical ledger, which records all incomings and outgoings, so I can see what you spend if I choose to ... but I want you to start considering this as your money now, and become comfortable enough to use it whenever and however you like ... as I said this morning ... within reason, obviously."