Typically, you're supposed to operate a fridge not more than 3 degrees off-level, left to right (looking at the front of the fridge), and not more than 6 degrees off-level, back to front. However, operating a fridge at or slightly below its max off-level spec is no guarantee it still won't suffer some slow, cumulative damage. Been there, done that. The only way to be absolutely sure your fridge is operating safely is by monitoring the flue temps. We take the stress out of off-level situations by monitoring our flue temps with an ARP Fridge Defend.