The number that only goes up.
Tell it what you were losing in a normal week. From your quit date it counts, second by second, the money that stayed in your account. Milestones land as things you can actually picture — new tires, a month of rent, the emergency fund you never got around to.
Log a relapse and the number adjusts honestly. It never resets to zero and it never lies to you to keep you opening the app.