Add example for synchronous gauge

metric/example_test.go

@@ -142,6 +142,35 @@ func ExampleMeter_upDownCounter() {
 	}
 }
 
+// Gauges can be used to record non-additive values when changes occur.
+//
+// Here's how you might report the current speed of a cpu fan.
+func ExampleMeter_gauge() {
+	speedGauge, err := meter.Int64Gauge(
+		"cpu.fan.speed",
+		metric.WithDescription("Speed of CPU fan"),
+		metric.WithUnit("RPM"),
+	)
+	if err != nil {
+		panic(err)
+	}
+
+	getCPUFanSpeed := func() int64 {
+		// hard-code 1500 RPM for demonstrative purposes
+		// do the real work to get the cpu fan speed
+		return 1500
+	}
+
+	_ = func() {
+		go func() {
+			for {
+				time.Sleep(time.Second * 3)
+				speedGauge.Record(context.Background(), getCPUFanSpeed())
+			}
+		}()
+	}
+}
+
 // Histograms are used to measure a distribution of values over time.
 //
 // Here's how you might report a distribution of response times for an HTTP handler.