type Gauge interface from pkg github.com/go-kit/kit/metrics has no field or method Add

hi guys i need help. i want to have reference on the current gauge using native prometheus (i don't want to implement it myself). since only method available on the interface in metrics package is Set i don't have any reference to the current gauge number.

is strange that pkg metrics/prometheus has Add method and pkg metrics don't?
is there an opinionated way to do this and am i missing something?
is it a generalization for other collectors aside from prometheus?
what's the correct way to Add in gauge (for prometheus)?