diff --git a/meter.go b/meter.go
index aa5e587..b70593e 100644
--- a/meter.go
+++ b/meter.go
@@ -33,6 +33,9 @@ func (s Snapshot) String() string {
 type Meter struct {
 	accumulator uint64
 
+	// managed by the sweeper loop.
+	registered bool
+
 	// Take lock.
 	snapshot Snapshot
 }
@@ -40,8 +43,9 @@ type Meter struct {
 // Mark updates the total.
 func (m *Meter) Mark(count uint64) {
 	if count > 0 && atomic.AddUint64(&m.accumulator, count) == count {
-		// I'm the first one to bump this above 0.
-		// Register it.
+		// The accumulator is 0 so we probably need to register. We may
+		// already _be_ registered however, if we are, the registration
+		// loop will notice that `m.registered` is set and ignore us.
 		globalSweeper.Register(m)
 	}
 }
@@ -53,6 +57,15 @@ func (m *Meter) Snapshot() Snapshot {
 	return m.snapshot
 }
 
+// Reset sets accumulator, total and rate to zero.
+func (m *Meter) Reset() {
+	globalSweeper.snapshotMu.Lock()
+	atomic.StoreUint64(&m.accumulator, 0)
+	m.snapshot.Rate = 0
+	m.snapshot.Total = 0
+	globalSweeper.snapshotMu.Unlock()
+}
+
 func (m *Meter) String() string {
 	return m.Snapshot().String()
 }
diff --git a/meter_test.go b/meter_test.go
index f0bd810..0f29a8e 100644
--- a/meter_test.go
+++ b/meter_test.go
@@ -3,6 +3,8 @@ package flow
 import (
 	"fmt"
 	"math"
+	"sync"
+	"testing"
 	"time"
 )
 
@@ -29,6 +31,43 @@ func ExampleMeter() {
 	// Output: 3000 (300/s)
 }
 
+func TestResetMeter(t *testing.T) {
+	meter := new(Meter)
+
+	meter.Mark(30)
+
+	time.Sleep(2 * time.Second)
+
+	if total := meter.Snapshot().Total; total != 30 {
+		t.Errorf("total = %d; want 30", total)
+	}
+
+	meter.Reset()
+
+	if total := meter.Snapshot().Total; total != 0 {
+		t.Errorf("total = %d; want 0", total)
+	}
+}
+
+func TestMarkResetMeterMulti(t *testing.T) {
+	var wg sync.WaitGroup
+	wg.Add(2)
+
+	meter := new(Meter)
+	go func(meter *Meter) {
+		meter.Mark(30)
+		meter.Mark(30)
+		wg.Done()
+	}(meter)
+
+	go func(meter *Meter) {
+		meter.Reset()
+		wg.Done()
+	}(meter)
+
+	wg.Wait()
+}
+
 func roundTens(x float64) int64 {
 	return int64(math.Floor(x/10+0.5)) * 10
 }
diff --git a/registry.go b/registry.go
index 81c8d85..d3e47be 100644
--- a/registry.go
+++ b/registry.go
@@ -72,3 +72,11 @@ func (r *MeterRegistry) ForEach(iterFunc func(string, *Meter)) {
 		return true
 	})
 }
+
+// Clear removes all meters from the registry.
+func (r *MeterRegistry) Clear() {
+	r.meters.Range(func(k, v interface{}) bool {
+		r.meters.Delete(k)
+		return true
+	})
+}
diff --git a/registry_test.go b/registry_test.go
index 5795029..f7976c9 100644
--- a/registry_test.go
+++ b/registry_test.go
@@ -15,7 +15,7 @@ func TestRegistry(t *testing.T) {
 	m1.Mark(10)
 	m2.Mark(30)
 
-	time.Sleep(2 * time.Second)
+	time.Sleep(2*time.Second + time.Millisecond)
 
 	if total := r.Get("first").Snapshot().Total; total != 10 {
 		t.Errorf("expected first total to be 10, got %d", total)
@@ -98,3 +98,27 @@ func TestRegistry(t *testing.T) {
 		t.Error("expected to trim 2 idle timers")
 	}
 }
+
+func TestClearRegistry(t *testing.T) {
+	r := new(MeterRegistry)
+	m1 := r.Get("first")
+	m2 := r.Get("second")
+
+	m1.Mark(10)
+	m2.Mark(30)
+
+	time.Sleep(2 * time.Second)
+
+	r.Clear()
+
+	r.ForEach(func(n string, _m *Meter) {
+		t.Errorf("expected no meters at all, found a meter %s", n)
+	})
+
+	if total := r.Get("first").Snapshot().Total; total != 0 {
+		t.Errorf("expected first total to be 0, got %d", total)
+	}
+	if total := r.Get("second").Snapshot().Total; total != 0 {
+		t.Errorf("expected second total to be 0, got %d", total)
+	}
+}
diff --git a/sweeper.go b/sweeper.go
index 48e301c..e4294ed 100644
--- a/sweeper.go
+++ b/sweeper.go
@@ -23,8 +23,9 @@ var globalSweeper sweeper
 type sweeper struct {
 	sweepOnce sync.Once
 
-	snapshotMu sync.RWMutex
-	meters     []*Meter
+	snapshotMu   sync.RWMutex
+	meters       []*Meter
+	activeMeters int
 
 	lastUpdateTime  time.Time
 	registerChannel chan *Meter
@@ -43,9 +44,11 @@ func (sw *sweeper) run() {
 }
 
 func (sw *sweeper) register(m *Meter) {
-	// Add back the snapshot total. If we unregistered this
-	// one, we set it to zero.
-	atomic.AddUint64(&m.accumulator, m.snapshot.Total)
+	if m.registered {
+		// registered twice, move on.
+		return
+	}
+	m.registered = true
 	sw.meters = append(sw.meters, m)
 }
 
@@ -85,9 +88,9 @@ func (sw *sweeper) update() {
 	sw.lastUpdateTime = now
 	timeMultiplier := float64(time.Second) / float64(tdiff)
 
+	// Calculate the bandwidth for all active meters.
 	newLen := len(sw.meters)
-
-	for i, m := range sw.meters {
+	for i, m := range sw.meters[:sw.activeMeters] {
 		total := atomic.LoadUint64(&m.accumulator)
 		diff := total - m.snapshot.Total
 		instant := timeMultiplier * float64(diff)
@@ -142,16 +145,31 @@ func (sw *sweeper) update() {
 		}
 
 		// Reset the rate, keep the total.
+		m.registered = false
 		m.snapshot.Rate = 0
 		newLen--
 		sw.meters[i] = sw.meters[newLen]
 	}
 
+	// Re-add the total to all the newly active accumulators and set the snapshot to the total.
+	// 1. We don't do this on register to avoid having to take the snapshot lock.
+	// 2. We skip calculating the bandwidth for this round so we get an _accurate_ bandwidth calculation.
+	for _, m := range sw.meters[sw.activeMeters:] {
+		total := atomic.AddUint64(&m.accumulator, m.snapshot.Total)
+		if total > m.snapshot.Total {
+			m.snapshot.LastUpdate = now
+		}
+		m.snapshot.Total = total
+	}
+
 	// trim the meter list
 	for i := newLen; i < len(sw.meters); i++ {
 		sw.meters[i] = nil
 	}
 	sw.meters = sw.meters[:newLen]
+
+	// Finally, mark all meters still in the list as "active".
+	sw.activeMeters = len(sw.meters)
 }
 
 func (sw *sweeper) Register(m *Meter) {