There are several aspects to it that aim to make it feel fair. First there's the credit system, and people who take less desirable shifts getting more credits, so they end up working fewer shifts in total. But there are also limitations on what the scheduling admin can do. E.g. they can't assign credits to themselves, or enter "block periods" (= a calendar time when someone is blocked from being assigned any shifts, e.g. because they're on parental leave or military leave, or something like that). There's also a "credit accounting log", which shows all the transactions in the system, and how those transactions changed the credit balances of all the rotation members. I hope (and think) that the kind of geeky game-prone people who work tech oncall jobs might appreciate the game-like nature of this system.