i have an aftermarket bung and sensor on my carb'd truck that runs a air/fuel mixture gauge. it was installed by a past owner and i'm not sure how accurate it is. it fluctuates when cold to warm and when you stomp the gas and when you let out of it.
i richened and leaned my carb adjustments(just to see),and it showed it on the gauge, but i pay very little attention to the gauge.