diff --git a/metric/instrument.go b/metric/instrument.go
index 0033c1e12..cdca00058 100644
--- a/metric/instrument.go
+++ b/metric/instrument.go
@@ -167,6 +167,8 @@ func (o unitOpt) applyInt64ObservableGauge(c Int64ObservableGaugeConfig) Int64Ob
 }
 
 // WithUnit sets the instrument unit.
+//
+// The unit u should be defined using the appropriate [UCUM](https://ucum.org) case-sensitive code.
 func WithUnit(u string) InstrumentOption { return unitOpt(u) }
 
 // AddOption applies options to an addition measurement. See