Put where you can see both of them at the same time when running the jacks (if you have a remote).
Mine are only a rough guide as they're "adjustable" lol. The foam tape actually allows them to move around a bit. Sometimes I adjust them to "level" after leveling, haha.
Typical of many "methods" on this forum, lets not pretend that the camper needs to be "perfectly" level. I suppose if a guy can't eyeball something relatively level then it's an issue. For me it's more of a guide when unloading to know how out of level I need to put the camper when re-loading (IE 4deg low in front, 3 deg low on the left), so the truck bed matches the camper when backing under it.
Your camper and fridge won't care it its off a couple percent, even long term and if you're not getting rolled out of bed and the limes stay on the counter, it's probably close enough.