diff --git a/container/container.go b/container/container.go
index b757ce86..7d21d1d1 100644
--- a/container/container.go
+++ b/container/container.go
@@ -35,12 +35,12 @@ type ContainerHandler interface {
 	ListContainers(listType ListType) ([]string, error)
 	ListThreads(listType ListType) ([]int, error)
 	ListProcesses(listType ListType) ([]int, error)
-	StatsSummary() (*info.ContainerStatsSummary, error)
+	StatsSummary() (*info.ContainerStatsPercentiles, error)
 }
 
 type NoStatsSummary struct {
 }
 
-func (self *NoStatsSummary) StatsSummary() (*info.ContainerStatsSummary, error) {
+func (self *NoStatsSummary) StatsSummary() (*info.ContainerStatsPercentiles, error) {
 	return nil, fmt.Errorf("This method (StatsSummary) should never be called")
 }
diff --git a/container/statssum.go b/container/statssum.go
index 6126b877..faa3c67d 100644
--- a/container/statssum.go
+++ b/container/statssum.go
@@ -15,7 +15,7 @@
 package container
 
 import (
-	"math/big"
+	"fmt"
 	"sync"
 	"time"
 
@@ -23,81 +23,104 @@ import (
 	"github.com/google/cadvisor/sampling"
 )
 
-type statsSummaryContainerHandlerWrapper struct {
-	handler          ContainerHandler
-	currentSummary   *info.ContainerStatsSummary
-	totalMemoryUsage *big.Int
-	numStats         uint64
-	sampler          sampling.Sampler
-	lock             sync.Mutex
+type percentilesContainerHandlerWrapper struct {
+	handler              ContainerHandler
+	containerPercentiles *info.ContainerStatsPercentiles
+	prevStats            *info.ContainerStats
+	numStats             uint64
+	sampler              sampling.Sampler
+	lock                 sync.Mutex
 }
 
-func (self *statsSummaryContainerHandlerWrapper) GetSpec() (*info.ContainerSpec, error) {
+func (self *percentilesContainerHandlerWrapper) GetSpec() (*info.ContainerSpec, error) {
 	return self.handler.GetSpec()
 }
 
-func (self *statsSummaryContainerHandlerWrapper) GetStats() (*info.ContainerStats, error) {
+func (self *percentilesContainerHandlerWrapper) updatePrevStats(stats *info.ContainerStats) {
+	if stats == nil || stats.Cpu == nil || stats.Memory == nil {
+		// discard incomplete stats
+		self.prevStats = nil
+		return
+	}
+	if self.prevStats == nil {
+		self.prevStats = &info.ContainerStats{
+			Cpu:    &info.CpuStats{},
+			Memory: &info.MemoryStats{},
+		}
+	}
+	// make a deep copy.
+	self.prevStats.Timestamp = stats.Timestamp
+	*self.prevStats.Cpu = *stats.Cpu
+	self.prevStats.Cpu.Usage.PerCpu = make([]uint64, len(stats.Cpu.Usage.PerCpu))
+	for i, perCpu := range stats.Cpu.Usage.PerCpu {
+		self.prevStats.Cpu.Usage.PerCpu[i] = perCpu
+	}
+	*self.prevStats.Memory = *stats.Memory
+}
+
+func (self *percentilesContainerHandlerWrapper) GetStats() (*info.ContainerStats, error) {
 	stats, err := self.handler.GetStats()
 	if err != nil {
 		return nil, err
 	}
 	if stats == nil {
-		return nil, nil
+		return nil, fmt.Errorf("container handler returns a nil error and a nil stats")
+	}
+	if stats.Timestamp.IsZero() {
+		return nil, fmt.Errorf("container handler did not set timestamp")
 	}
-	stats.Timestamp = time.Now()
 	self.lock.Lock()
 	defer self.lock.Unlock()
 
-	self.sampler.Update(stats)
-	if self.currentSummary == nil {
-		self.currentSummary = new(info.ContainerStatsSummary)
+	if self.prevStats != nil {
+		sample, err := info.NewSample(self.prevStats, stats)
+		if err != nil {
+			return nil, fmt.Errorf("wrong stats: %v", err)
+		}
+		if sample != nil {
+			self.sampler.Update(sample)
+		}
+	}
+	self.updatePrevStats(stats)
+	if self.containerPercentiles == nil {
+		self.containerPercentiles = new(info.ContainerStatsPercentiles)
 	}
 	self.numStats++
 	if stats.Memory != nil {
-		if stats.Memory.Usage > self.currentSummary.MaxMemoryUsage {
-			self.currentSummary.MaxMemoryUsage = stats.Memory.Usage
+		if stats.Memory.Usage > self.containerPercentiles.MaxMemoryUsage {
+			self.containerPercentiles.MaxMemoryUsage = stats.Memory.Usage
 		}
-
-		// XXX(dengnan): Very inefficient!
-		if self.totalMemoryUsage == nil {
-			self.totalMemoryUsage = new(big.Int)
-		}
-		usage := (&big.Int{}).SetUint64(stats.Memory.Usage)
-		self.totalMemoryUsage = self.totalMemoryUsage.Add(self.totalMemoryUsage, usage)
-		n := (&big.Int{}).SetUint64(self.numStats)
-		avg := (&big.Int{}).Div(self.totalMemoryUsage, n)
-		self.currentSummary.AvgMemoryUsage = avg.Uint64()
 	}
 	return stats, nil
 }
 
-func (self *statsSummaryContainerHandlerWrapper) ListContainers(listType ListType) ([]string, error) {
+func (self *percentilesContainerHandlerWrapper) ListContainers(listType ListType) ([]string, error) {
 	return self.handler.ListContainers(listType)
 }
 
-func (self *statsSummaryContainerHandlerWrapper) ListThreads(listType ListType) ([]int, error) {
+func (self *percentilesContainerHandlerWrapper) ListThreads(listType ListType) ([]int, error) {
 	return self.handler.ListThreads(listType)
 }
 
-func (self *statsSummaryContainerHandlerWrapper) ListProcesses(listType ListType) ([]int, error) {
+func (self *percentilesContainerHandlerWrapper) ListProcesses(listType ListType) ([]int, error) {
 	return self.handler.ListProcesses(listType)
 }
 
-func (self *statsSummaryContainerHandlerWrapper) StatsSummary() (*info.ContainerStatsSummary, error) {
+func (self *percentilesContainerHandlerWrapper) StatsSummary() (*info.ContainerStatsPercentiles, error) {
 	self.lock.Lock()
 	defer self.lock.Unlock()
-	samples := make([]*info.ContainerStats, 0, self.sampler.Len())
+	samples := make([]*info.ContainerStatsSample, 0, self.sampler.Len())
 	self.sampler.Map(func(d interface{}) {
-		stats := d.(*info.ContainerStats)
+		stats := d.(*info.ContainerStatsSample)
 		samples = append(samples, stats)
 	})
-	self.currentSummary.Samples = samples
+	self.containerPercentiles.Samples = samples
 	// XXX(dengnan): propabily add to StatsParameter?
-	self.currentSummary.FillPercentiles(
+	self.containerPercentiles.FillPercentiles(
 		[]int{50, 80, 90, 95, 99},
 		[]int{50, 80, 90, 95, 99},
 	)
-	return self.currentSummary, nil
+	return self.containerPercentiles, nil
 }
 
 type StatsParameter struct {
@@ -112,9 +135,9 @@ func AddStatsSummary(handler ContainerHandler, parameter *StatsParameter) (Conta
 	if err != nil {
 		return nil, err
 	}
-	return &statsSummaryContainerHandlerWrapper{
-		handler:        handler,
-		currentSummary: &info.ContainerStatsSummary{},
-		sampler:        sampler,
+	return &percentilesContainerHandlerWrapper{
+		handler:              handler,
+		containerPercentiles: &info.ContainerStatsPercentiles{},
+		sampler:              sampler,
 	}, nil
 }
diff --git a/container/statssum_test.go b/container/statssum_test.go
index 07adcac6..7385bd2b 100644
--- a/container/statssum_test.go
+++ b/container/statssum_test.go
@@ -15,53 +15,40 @@
 package container
 
 import (
-	crand "crypto/rand"
-	"encoding/binary"
 	"math/rand"
+	"sync"
 	"testing"
+	"time"
 
 	"github.com/google/cadvisor/info"
 )
 
-func init() {
-	// NOTE(dengnan): Even if we picked a good random seed,
-	// the random number from math/rand is still not cryptographically secure!
-	var seed int64
-	binary.Read(crand.Reader, binary.LittleEndian, &seed)
-	rand.Seed(seed)
+type mockContainer struct {
 }
 
-type randomStatsContainer struct {
-	NoStatsSummary
+func (self *mockContainer) GetSpec() (*info.ContainerSpec, error) {
+	return nil, nil
 }
-
-func (self *randomStatsContainer) GetSpec() (*info.ContainerSpec, error) {
+func (self *mockContainer) ListContainers(listType ListType) ([]string, error) {
 	return nil, nil
 }
 
-func (self *randomStatsContainer) GetStats() (*info.ContainerStats, error) {
-	stats := new(info.ContainerStats)
-	stats.Cpu = new(info.CpuStats)
-	stats.Memory = new(info.MemoryStats)
-	stats.Memory.Usage = uint64(rand.Intn(2048))
-	return stats, nil
-}
-
-func (self *randomStatsContainer) ListContainers(listType ListType) ([]string, error) {
+func (self *mockContainer) ListThreads(listType ListType) ([]int, error) {
 	return nil, nil
 }
 
-func (self *randomStatsContainer) ListThreads(listType ListType) ([]int, error) {
+func (self *mockContainer) ListProcesses(listType ListType) ([]int, error) {
 	return nil, nil
 }
 
-func (self *randomStatsContainer) ListProcesses(listType ListType) ([]int, error) {
-	return nil, nil
-}
-
-func TestAvgMaxMemoryUsage(t *testing.T) {
+func TestMaxMemoryUsage(t *testing.T) {
+	N := 100
+	memTrace := make([]uint64, N)
+	for i := 0; i < N; i++ {
+		memTrace[i] = uint64(i + 1)
+	}
 	handler, err := AddStatsSummary(
-		&randomStatsContainer{},
+		containerWithTrace(1*time.Second, nil, memTrace),
 		&StatsParameter{
 			Sampler:    "uniform",
 			NumSamples: 10,
@@ -70,19 +57,13 @@ func TestAvgMaxMemoryUsage(t *testing.T) {
 	if err != nil {
 		t.Error(err)
 	}
-	var maxUsage uint64
-	var totalUsage uint64
-	N := 100
+	maxUsage := uint64(N)
 	for i := 0; i < N; i++ {
-		stats, err := handler.GetStats()
+		_, err := handler.GetStats()
 		if err != nil {
 			t.Errorf("Error when get stats: %v", err)
 			continue
 		}
-		if stats.Memory.Usage > maxUsage {
-			maxUsage = stats.Memory.Usage
-		}
-		totalUsage += stats.Memory.Usage
 	}
 	summary, err := handler.StatsSummary()
 	if err != nil {
@@ -91,8 +72,109 @@ func TestAvgMaxMemoryUsage(t *testing.T) {
 	if summary.MaxMemoryUsage != maxUsage {
 		t.Fatalf("Max memory usage should be %v; received %v", maxUsage, summary.MaxMemoryUsage)
 	}
-	avg := totalUsage / uint64(N)
-	if summary.AvgMemoryUsage != avg {
-		t.Fatalf("Avg memory usage should be %v; received %v", avg, summary.AvgMemoryUsage)
+}
+
+type replayTrace struct {
+	NoStatsSummary
+	mockContainer
+	cpuTrace    []uint64
+	memTrace    []uint64
+	totalUsage  uint64
+	currenttime time.Time
+	duration    time.Duration
+	lock        sync.Mutex
+}
+
+func containerWithTrace(duration time.Duration, cpuUsages []uint64, memUsages []uint64) ContainerHandler {
+	return &replayTrace{
+		duration:    duration,
+		cpuTrace:    cpuUsages,
+		memTrace:    memUsages,
+		currenttime: time.Now(),
+	}
+}
+
+func (self *replayTrace) GetStats() (*info.ContainerStats, error) {
+	stats := new(info.ContainerStats)
+	stats.Cpu = new(info.CpuStats)
+	stats.Memory = new(info.MemoryStats)
+	if len(self.memTrace) > 0 {
+		stats.Memory.Usage = self.memTrace[0]
+		self.memTrace = self.memTrace[1:]
+	}
+
+	self.lock.Lock()
+	defer self.lock.Unlock()
+
+	cpuTrace := self.totalUsage
+	if len(self.cpuTrace) > 0 {
+		cpuTrace += self.cpuTrace[0]
+		self.cpuTrace = self.cpuTrace[1:]
+	}
+	self.totalUsage = cpuTrace
+	stats.Timestamp = self.currenttime
+	self.currenttime = self.currenttime.Add(self.duration)
+	stats.Cpu.Usage.Total = cpuTrace
+	stats.Cpu.Usage.PerCpu = []uint64{cpuTrace}
+	stats.Cpu.Usage.User = cpuTrace
+	stats.Cpu.Usage.System = 0
+	return stats, nil
+}
+
+func TestSampleCpuUsage(t *testing.T) {
+	// Number of samples
+	N := 10
+	cpuTrace := make([]uint64, 0, N)
+	memTrace := make([]uint64, 0, N)
+
+	// We need N+1 observations to get N samples
+	for i := 0; i < N+1; i++ {
+		cpuusage := uint64(rand.Intn(1000))
+		memusage := uint64(rand.Intn(1000))
+		cpuTrace = append(cpuTrace, cpuusage)
+		memTrace = append(memTrace, memusage)
+	}
+
+	samplePeriod := 1 * time.Second
+
+	handler, err := AddStatsSummary(
+		containerWithTrace(samplePeriod, cpuTrace, memTrace),
+		&StatsParameter{
+			// Use uniform sampler with sample size of N, so that
+			// we will be guaranteed to store the first N samples.
+			Sampler:    "uniform",
+			NumSamples: N,
+		},
+	)
+	if err != nil {
+		t.Error(err)
+	}
+
+	// request stats/obervation N+1 times, so that there will be N samples
+	for i := 0; i < N+1; i++ {
+		_, err = handler.GetStats()
+		if err != nil {
+			t.Fatal(err)
+		}
+	}
+
+	s, err := handler.StatsSummary()
+	if err != nil {
+		t.Fatal(err)
+	}
+	for _, sample := range s.Samples {
+		if sample.Duration != samplePeriod {
+			t.Errorf("sample duration is %v, not %v", sample.Duration, samplePeriod)
+		}
+		cpuUsage := sample.Cpu.Usage
+		found := false
+		for _, u := range cpuTrace {
+			if u == cpuUsage {
+				found = true
+			}
+		}
+		if !found {
+			t.Errorf("unable to find cpu usage %v", cpuUsage)
+		}
 	}
 }
diff --git a/info/container.go b/info/container.go
index 3f4f8e72..16e47442 100644
--- a/info/container.go
+++ b/info/container.go
@@ -15,6 +15,7 @@
 package info
 
 import (
+	"fmt"
 	"sort"
 	"time"
 )
@@ -61,7 +62,7 @@ type ContainerInfo struct {
 	// Historical statistics gathered from the container.
 	Stats []*ContainerStats `json:"stats,omitempty"`
 
-	StatsSummary *ContainerStatsSummary `json:"stats_summary,omitempty"`
+	StatsSummary *ContainerStatsPercentiles `json:"stats_summary,omitempty"`
 }
 
 func (self *ContainerInfo) StatsAfter(ref time.Time) []*ContainerStats {
@@ -99,12 +100,24 @@ func (self *ContainerInfo) StatsEndTime() time.Time {
 	return ret
 }
 
+// All CPU usage metrics are cumulative from the creation of the container
 type CpuStats struct {
 	Usage struct {
-		Total  uint64   `json:"total"`
+		// Total CPU usage.
+		// Units: nanoseconds
+		Total uint64 `json:"total"`
+
+		// Per CPU/core usage of the container.
+		// Unit: nanoseconds.
 		PerCpu []uint64 `json:"per_cpu,omitempty"`
-		User   uint64   `json:"user"`
-		System uint64   `json:"system"`
+
+		// Time spent in user space.
+		// Unit: nanoseconds
+		User uint64 `json:"user"`
+
+		// Time spent in kernel space.
+		// Unit: nanoseconds
+		System uint64 `json:"system"`
 	} `json:"usage"`
 	Load int32 `json:"load"`
 }
@@ -142,6 +155,21 @@ type ContainerStats struct {
 	Memory    *MemoryStats `json:"memory,omitempty"`
 }
 
+type ContainerStatsSample struct {
+	// Timetamp of the end of the sample period
+	Timestamp time.Time `json:"timestamp"`
+	// Duration of the sample period
+	Duration time.Duration `json:"duration"`
+	Cpu      struct {
+		// number of nanoseconds of CPU time used by the container
+		Usage uint64 `json:"usage"`
+	} `json:"cpu"`
+	Memory struct {
+		// Units: Bytes.
+		Usage uint64 `json:"usage"`
+	} `json:"memory"`
+}
+
 // This is not exported.
 // Use FillPercentile to calculate percentiles
 type percentile struct {
@@ -149,13 +177,43 @@ type percentile struct {
 	Value      uint64 `json:"value"`
 }
 
-type ContainerStatsSummary struct {
+type ContainerStatsPercentiles struct {
 	// TODO(dengnan): More things?
-	MaxMemoryUsage         uint64            `json:"max_memory_usage,omitempty"`
-	AvgMemoryUsage         uint64            `json:"avg_memory_usage,omitempty"`
-	Samples                []*ContainerStats `json:"samples,omitempty"`
-	MemoryUsagePercentiles []percentile      `json:"memory_usage_percentiles,omitempty"`
-	CpuUsagePercentiles    []percentile      `json:"cpu_usage_percentiles,omitempty"`
+	MaxMemoryUsage         uint64                  `json:"max_memory_usage,omitempty"`
+	Samples                []*ContainerStatsSample `json:"samples,omitempty"`
+	MemoryUsagePercentiles []percentile            `json:"memory_usage_percentiles,omitempty"`
+	CpuUsagePercentiles    []percentile            `json:"cpu_usage_percentiles,omitempty"`
+}
+
+// Each sample needs two stats because the cpu usage in ContainerStats is
+// cumulative.
+// prev should be an earlier observation than current.
+// This method is not thread/goroutine safe.
+func NewSample(prev, current *ContainerStats) (*ContainerStatsSample, error) {
+	if prev == nil || current == nil {
+		return nil, fmt.Errorf("empty stats")
+	}
+	// Ignore this sample if it is incomplete
+	if prev.Cpu == nil || prev.Memory == nil || current.Cpu == nil || current.Memory == nil {
+		return nil, fmt.Errorf("incomplete stats")
+	}
+	// prev must be an early observation
+	if !current.Timestamp.After(prev.Timestamp) {
+		return nil, fmt.Errorf("wrong stats order")
+	}
+	// This data is invalid.
+	if current.Cpu.Usage.Total < prev.Cpu.Usage.Total {
+		return nil, fmt.Errorf("current CPU usage is less than prev CPU usage (cumulative).")
+	}
+	sample := new(ContainerStatsSample)
+	// Caculate the diff to get the CPU usage within the time interval.
+	sample.Cpu.Usage = current.Cpu.Usage.Total - prev.Cpu.Usage.Total
+	// Memory usage is current memory usage
+	sample.Memory.Usage = current.Memory.Usage
+	sample.Timestamp = current.Timestamp
+	sample.Duration = current.Timestamp.Sub(prev.Timestamp)
+
+	return sample, nil
 }
 
 type uint64Slice []uint64
@@ -172,40 +230,26 @@ func (self uint64Slice) Swap(i, j int) {
 	self[i], self[j] = self[j], self[i]
 }
 
-func (self uint64Slice) Percentiles(ps ...int) []uint64 {
+func (self uint64Slice) Percentiles(requestedPercentiles ...int) []percentile {
 	if len(self) == 0 {
 		return nil
 	}
-	ret := make([]uint64, 0, len(ps))
+	ret := make([]percentile, 0, len(requestedPercentiles))
 	sort.Sort(self)
-	for _, p := range ps {
-		idx := (float64(p) / 100.0) * float64(len(self)+1)
-		if idx > float64(len(self)-1) {
-			ret = append(ret, self[len(self)-1])
-		} else {
-			ret = append(ret, self[int(idx)])
-		}
+	for _, p := range requestedPercentiles {
+		idx := (len(self) * p / 100) - 1
+		ret = append(
+			ret,
+			percentile{
+				Percentage: p,
+				Value:      self[idx],
+			},
+		)
 	}
 	return ret
 }
 
-// len(bs) <= len(as)
-func float64Zipuint64(as []int, bs []uint64) []percentile {
-	if len(bs) == 0 {
-		return nil
-	}
-	ret := make([]percentile, len(bs))
-	for i, b := range bs {
-		a := as[i]
-		ret[i] = percentile{
-			Percentage: a,
-			Value:      b,
-		}
-	}
-	return ret
-}
-
-func (self *ContainerStatsSummary) FillPercentiles(cpuPercentages, memoryPercentages []int) {
+func (self *ContainerStatsPercentiles) FillPercentiles(cpuPercentages, memoryPercentages []int) {
 	if len(self.Samples) == 0 {
 		return
 	}
@@ -216,16 +260,10 @@ func (self *ContainerStatsSummary) FillPercentiles(cpuPercentages, memoryPercent
 		if sample == nil {
 			continue
 		}
-		if sample.Cpu != nil {
-			cpuUsages = append(cpuUsages, sample.Cpu.Usage.Total)
-		}
-		if sample.Memory != nil {
-			memUsages = append(memUsages, sample.Memory.Usage)
-		}
+		cpuUsages = append(cpuUsages, sample.Cpu.Usage)
+		memUsages = append(memUsages, sample.Memory.Usage)
 	}
 
-	cpuPercentiles := uint64Slice(cpuUsages).Percentiles(cpuPercentages...)
-	memPercentiles := uint64Slice(memUsages).Percentiles(memoryPercentages...)
-	self.CpuUsagePercentiles = float64Zipuint64(cpuPercentages, cpuPercentiles)
-	self.MemoryUsagePercentiles = float64Zipuint64(memoryPercentages, memPercentiles)
+	self.CpuUsagePercentiles = uint64Slice(cpuUsages).Percentiles(cpuPercentages...)
+	self.MemoryUsagePercentiles = uint64Slice(memUsages).Percentiles(memoryPercentages...)
 }
diff --git a/info/container_test.go b/info/container_test.go
index 3c0d7342..fde9ab41 100644
--- a/info/container_test.go
+++ b/info/container_test.go
@@ -67,20 +67,152 @@ func TestPercentiles(t *testing.T) {
 	N := 100
 	data := make([]uint64, N)
 
-	for i := 0; i < N; i++ {
-		data[i] = uint64(i)
+	for i := 1; i < N+1; i++ {
+		data[i-1] = uint64(i)
 	}
-	ps := []float64{
-		0.8,
-		0.9,
-		0.5,
+	percentages := []int{
+		80,
+		90,
+		50,
 	}
-	ss := uint64Slice(data).Percentiles(ps...)
-	for i, s := range ss {
-		p := ps[i]
-		d := uint64(float64(N) * p)
-		if d != s {
-			t.Errorf("%v \\%tile data should be %v, but got %v", p*float64(100), d, s)
+	percentiles := uint64Slice(data).Percentiles(percentages...)
+	for _, s := range percentiles {
+		if s.Value != uint64(s.Percentage) {
+			t.Errorf("%v percentile data should be %v, but got %v", s.Percentage, s.Percentage, s.Value)
 		}
+		/*
+			p := percentages[i]
+			d := uint64(N * p / 100)
+			if d != s {
+				t.Errorf("%v percentile data should be %v, but got %v", p, d, s)
+			}
+		*/
+	}
+}
+
+func TestNewSampleNilStats(t *testing.T) {
+	stats := &ContainerStats{
+		Cpu:    &CpuStats{},
+		Memory: &MemoryStats{},
+	}
+	stats.Cpu.Usage.PerCpu = []uint64{uint64(10)}
+	stats.Cpu.Usage.Total = uint64(10)
+	stats.Cpu.Usage.System = uint64(2)
+	stats.Cpu.Usage.User = uint64(8)
+	stats.Memory.Usage = uint64(200)
+
+	sample, err := NewSample(nil, stats)
+	if err == nil {
+		t.Errorf("generated an unexpected sample: %+v", sample)
+	}
+
+	sample, err = NewSample(stats, nil)
+	if err == nil {
+		t.Errorf("generated an unexpected sample: %+v", sample)
+	}
+}
+
+func createStats(cpuUsage, memUsage uint64, timestamp time.Time) *ContainerStats {
+	stats := &ContainerStats{
+		Cpu:    &CpuStats{},
+		Memory: &MemoryStats{},
+	}
+	stats.Cpu.Usage.PerCpu = []uint64{cpuUsage}
+	stats.Cpu.Usage.Total = cpuUsage
+	stats.Cpu.Usage.System = 0
+	stats.Cpu.Usage.User = cpuUsage
+	stats.Memory.Usage = memUsage
+	stats.Timestamp = timestamp
+	return stats
+}
+
+func TestAddSample(t *testing.T) {
+	cpuPrevUsage := uint64(10)
+	cpuCurrentUsage := uint64(15)
+	memCurrentUsage := uint64(200)
+	prevTime := time.Now()
+
+	prev := createStats(cpuPrevUsage, memCurrentUsage, prevTime)
+	current := createStats(cpuCurrentUsage, memCurrentUsage, prevTime.Add(1*time.Second))
+
+	sample, err := NewSample(prev, current)
+	if err != nil {
+		t.Errorf("should be able to generate a sample. but received error: %v", err)
+	}
+	if sample == nil {
+		t.Fatalf("nil sample and nil error. unexpected result!")
+	}
+
+	if sample.Memory.Usage != memCurrentUsage {
+		t.Errorf("wrong memory usage: %v. should be %v", sample.Memory.Usage, memCurrentUsage)
+	}
+
+	if sample.Cpu.Usage != cpuCurrentUsage-cpuPrevUsage {
+		t.Errorf("wrong CPU usage: %v. should be %v", sample.Cpu.Usage, cpuCurrentUsage-cpuPrevUsage)
+	}
+}
+
+func TestAddSampleIncompleteStats(t *testing.T) {
+	cpuPrevUsage := uint64(10)
+	cpuCurrentUsage := uint64(15)
+	memCurrentUsage := uint64(200)
+	prevTime := time.Now()
+
+	prev := createStats(cpuPrevUsage, memCurrentUsage, prevTime)
+	current := createStats(cpuCurrentUsage, memCurrentUsage, prevTime.Add(1*time.Second))
+	stats := &ContainerStats{
+		Cpu:    prev.Cpu,
+		Memory: nil,
+	}
+	sample, err := NewSample(stats, current)
+	if err == nil {
+		t.Errorf("generated an unexpected sample: %+v", sample)
+	}
+	sample, err = NewSample(prev, stats)
+	if err == nil {
+		t.Errorf("generated an unexpected sample: %+v", sample)
+	}
+
+	stats = &ContainerStats{
+		Cpu:    nil,
+		Memory: prev.Memory,
+	}
+	sample, err = NewSample(stats, current)
+	if err == nil {
+		t.Errorf("generated an unexpected sample: %+v", sample)
+	}
+	sample, err = NewSample(prev, stats)
+	if err == nil {
+		t.Errorf("generated an unexpected sample: %+v", sample)
+	}
+}
+
+func TestAddSampleWrongOrder(t *testing.T) {
+	cpuPrevUsage := uint64(10)
+	cpuCurrentUsage := uint64(15)
+	memCurrentUsage := uint64(200)
+	prevTime := time.Now()
+
+	prev := createStats(cpuPrevUsage, memCurrentUsage, prevTime)
+	current := createStats(cpuCurrentUsage, memCurrentUsage, prevTime.Add(1*time.Second))
+
+	sample, err := NewSample(current, prev)
+	if err == nil {
+		t.Errorf("generated an unexpected sample: %+v", sample)
+	}
+}
+
+func TestAddSampleWrongCpuUsage(t *testing.T) {
+	cpuPrevUsage := uint64(15)
+	cpuCurrentUsage := uint64(10)
+	memCurrentUsage := uint64(200)
+	prevTime := time.Now()
+
+	prev := createStats(cpuPrevUsage, memCurrentUsage, prevTime)
+	current := createStats(cpuCurrentUsage, memCurrentUsage, prevTime.Add(1*time.Second))
+
+	sample, err := NewSample(prev, current)
+	if err == nil {
+		t.Errorf("generated an unexpected sample: %+v", sample)
 	}
 }
diff --git a/manager/container.go b/manager/container.go
index b167b049..be7eea1e 100644
--- a/manager/container.go
+++ b/manager/container.go
@@ -39,7 +39,7 @@ type containerInfo struct {
 	Subcontainers []string
 	Spec          *info.ContainerSpec
 	Stats         *list.List
-	StatsSummary  *info.ContainerStatsSummary
+	StatsSummary  *info.ContainerStatsPercentiles
 }
 
 type containerData struct {