diff --git a/metrics/expvar/expvar_test.go b/metrics/expvar/expvar_test.go
index 34dc918..b6e3bf4 100644
--- a/metrics/expvar/expvar_test.go
+++ b/metrics/expvar/expvar_test.go
@@ -1,6 +1,8 @@
 package expvar_test
 
 import (
+	stdexpvar "expvar"
+	"fmt"
 	"testing"
 
 	"github.com/peterbourgon/gokit/metrics/expvar"
@@ -16,3 +18,12 @@
 	teststat.PopulateNormalHistogram(t, h, seed, mean, stdev)
 	teststat.AssertExpvarNormalHistogram(t, metricName, mean, stdev, quantiles)
 }
+
+func TestCallbackGauge(t *testing.T) {
+	value := 42.43
+	metricName := "foo"
+	expvar.PublishCallbackGauge(metricName, func() float64 { return value })
+	if want, have := fmt.Sprint(value), stdexpvar.Get(metricName).String(); want != have {
+		t.Errorf("want %q, have %q", want, have)
+	}
+}
diff --git a/metrics/prometheus/prometheus_test.go b/metrics/prometheus/prometheus_test.go
index a92a046..b6058cf 100644
--- a/metrics/prometheus/prometheus_test.go
+++ b/metrics/prometheus/prometheus_test.go
@@ -66,6 +66,19 @@
 	}
 }
 
+func TestPrometheusCallbackGauge(t *testing.T) {
+	value := 123.456
+	cb := func() float64 { return value }
+	prometheus.RegisterCallbackGauge("test", "prometheus_gauge", "bazbaz", "Help string.", cb)
+	if want, have := strings.Join([]string{
+		`# HELP test_prometheus_gauge_bazbaz Help string.`,
+		`# TYPE test_prometheus_gauge_bazbaz gauge`,
+		`test_prometheus_gauge_bazbaz 123.456`,
+	}, "\n"), teststat.ScrapePrometheus(t); !strings.Contains(have, want) {
+		t.Errorf("metric stanza not found or incorrect\n%s", have)
+	}
+}
+
 func TestPrometheusHistogram(t *testing.T) {
 	h := prometheus.NewHistogram("test", "prometheus_histogram", "foobar", "Qwerty asdf.", []string{})
 
diff --git a/metrics/statsd/statsd.go b/metrics/statsd/statsd.go
index 9146f25..6b7faf9 100644
--- a/metrics/statsd/statsd.go
+++ b/metrics/statsd/statsd.go
@@ -78,16 +78,17 @@
 // It collects values every scrape interval from the callback. Values are
 // buffered for the report interval or until the buffer exceeds a max packet
 // size, whichever comes first. The report and scrape intervals may be the
-// same. Fields are ignored.
+// same. The callback determines the value, and fields are ignored, so
+// NewCallbackGauge returns nothing.
 func NewCallbackGauge(w io.Writer, key string, reportInterval, scrapeInterval time.Duration, callback func() float64) {
 	go fwd(w, key, reportInterval, emitEvery(scrapeInterval, callback))
 }
 
-func emitEvery(d time.Duration, f func() float64) <-chan string {
+func emitEvery(d time.Duration, callback func() float64) <-chan string {
 	c := make(chan string)
 	go func() {
-		for range time.Tick(d) {
-			c <- fmt.Sprintf("%f|g", f())
+		for range tick(d) {
+			c <- fmt.Sprintf("%f|g", callback())
 		}
 	}()
 	return c
diff --git a/metrics/statsd/statsd_test.go b/metrics/statsd/statsd_test.go
index 46a2380..351e871 100644
--- a/metrics/statsd/statsd_test.go
+++ b/metrics/statsd/statsd_test.go
@@ -4,6 +4,7 @@
 
 import (
 	"bytes"
+	"fmt"
 	"runtime"
 	"testing"
 	"time"
@@ -38,31 +39,54 @@
 	buf := &bytes.Buffer{}
 	g := NewGauge(buf, "test_statsd_gauge", time.Second)
 
-	g.Add(1)          // send command
+	delta := 1.0
+	g.Add(delta)      // send command
 	runtime.Gosched() // yield to buffer write
 	ch <- time.Now()  // signal flush
 	runtime.Gosched() // yield to flush
-	if want, have := "test_statsd_gauge:+1.000000|g\n", buf.String(); want != have {
+	if want, have := fmt.Sprintf("test_statsd_gauge:+%f|g\n", delta), buf.String(); want != have {
 		t.Errorf("want %q, have %q", want, have)
 	}
 
 	buf.Reset()
 
-	g.Add(-2)
+	delta = -2.0
+	g.Add(delta)
 	runtime.Gosched()
 	ch <- time.Now()
 	runtime.Gosched()
-	if want, have := "test_statsd_gauge:-2.000000|g\n", buf.String(); want != have {
+	if want, have := fmt.Sprintf("test_statsd_gauge:%f|g\n", delta), buf.String(); want != have {
 		t.Errorf("want %q, have %q", want, have)
 	}
 
 	buf.Reset()
 
-	g.Set(3)
+	value := 3.0
+	g.Set(value)
 	runtime.Gosched()
 	ch <- time.Now()
 	runtime.Gosched()
-	if want, have := "test_statsd_gauge:3.000000|g\n", buf.String(); want != have {
+	if want, have := fmt.Sprintf("test_statsd_gauge:%f|g\n", value), buf.String(); want != have {
+		t.Errorf("want %q, have %q", want, have)
+	}
+}
+
+func TestCallbackGauge(t *testing.T) {
+	ch := make(chan time.Time)
+	tick = func(time.Duration) <-chan time.Time { return ch }
+	defer func() { tick = time.Tick }()
+
+	buf := &bytes.Buffer{}
+	value := 55.55
+	cb := func() float64 { return value }
+	NewCallbackGauge(buf, "test_statsd_callback_gauge", time.Second, time.Nanosecond, cb)
+
+	ch <- time.Now()  // signal emitter
+	runtime.Gosched() // yield to emitter
+	ch <- time.Now()  // signal flush
+	runtime.Gosched() // yield to flush
+
+	if want, have := fmt.Sprintf("test_statsd_callback_gauge:%f|g\n", value), buf.String(); want != have {
 		t.Errorf("want %q, have %q", want, have)
 	}
 }