diff --git a/bollinger_band_series.go b/bollinger_band_series.go
index 2894cdf..3529aa5 100644
--- a/bollinger_band_series.go
+++ b/bollinger_band_series.go
@@ -42,6 +42,17 @@ func (bbs BollingerBandsSeries) GetWindowSize(defaults ...int) int {
 	return bbs.WindowSize
 }
 
+// GetK returns the K value.
+func (bbs BollingerBandsSeries) GetK(defaults ...float64) float64 {
+	if bbs.K == 0 {
+		if len(defaults) > 0 {
+			return defaults[0]
+		}
+		return 2.0
+	}
+	return bbs.K
+}
+
 // Len returns the number of elements in the series.
 func (bbs *BollingerBandsSeries) Len() int {
 	return bbs.InnerSeries.Len()
@@ -65,8 +76,8 @@ func (bbs *BollingerBandsSeries) GetBoundedValue(index int) (x, y1, y2 float64)
 	ay := bbs.getAverage(bbs.valueBuffer)
 	std := bbs.getStdDev(bbs.valueBuffer)
 
-	y1 = ay + (bbs.K * std)
-	y2 = ay - (bbs.K * std)
+	y1 = ay + (bbs.GetK() * std)
+	y2 = ay - (bbs.GetK() * std)
 	return
 }
 
diff --git a/bollinger_band_series_test.go b/bollinger_band_series_test.go
new file mode 100644
index 0000000..5394afd
--- /dev/null
+++ b/bollinger_band_series_test.go
@@ -0,0 +1,32 @@
+package chart
+
+import (
+	"testing"
+
+	"github.com/blendlabs/go-assert"
+)
+
+func TestBollingerBandSeries(t *testing.T) {
+	assert := assert.New(t)
+
+	s1 := mockValueProvider{
+		X: Seq(1.0, 100.0),
+		Y: SeqRand(100, 1024),
+	}
+
+	bbs := &BollingerBandsSeries{
+		InnerSeries: s1,
+	}
+
+	xvalues := make([]float64, 100)
+	y1values := make([]float64, 100)
+	y2values := make([]float64, 100)
+
+	for x := 0; x < 100; x++ {
+		xvalues[x], y1values[x], y2values[x] = bbs.GetBoundedValue(x)
+	}
+
+	for x := bbs.GetWindowSize(); x < 100; x++ {
+		assert.True(y1values[x] > y2values[x])
+	}
+}
diff --git a/util.go b/util.go
index ac440f8..1e4e6ca 100644
--- a/util.go
+++ b/util.go
@@ -3,6 +3,7 @@ package chart
 import (
 	"fmt"
 	"math"
+	"math/rand"
 	"time"
 )
 
@@ -143,6 +144,18 @@ func Seq(start, end float64, steps ...float64) []float64 {
 	return values
 }
 
+// SeqRand generates a random sequence.
+func SeqRand(samples int, scale float64) []float64 {
+	rnd := rand.New(rand.NewSource(time.Now().Unix()))
+	values := make([]float64, samples)
+
+	for x := 0; x < samples; x++ {
+		values[x] = rnd.Float64() * scale
+	}
+
+	return values
+}
+
 // PercentDifference computes the percentage difference between two values.
 // The formula is (v2-v1)/v1.
 func PercentDifference(v1, v2 float64) float64 {