diff --git a/attitude/data.go b/attitude/attitude.go
similarity index 60%
rename from attitude/data.go
rename to attitude/attitude.go
index 760c5bf..71a9c95 100644
--- a/attitude/data.go
+++ b/attitude/attitude.go
@@ -4,14 +4,16 @@ import (
 	"fmt"
 )
 
-type Data struct {
+// Attitude describes the drones position relative to the ground.
+type Attitude struct {
 	Roll     float64 // degree
 	Pitch    float64 // degree
 	Yaw      float64 // degree
 	Altitude float64 // meters
 }
 
-func (d Data) String() string {
+// String returns a human readable version of the Attitude.
+func (d Attitude) String() string {
 	return fmt.Sprintf(
 		"Roll: %+6.1f Pitch: %+6.1f Yaw: %+6.1f Altitude: %+6.1f",
 		d.Roll,
diff --git a/attitude/complementary.go b/attitude/complementary.go
index b2a4022..c4004e9 100644
--- a/attitude/complementary.go
+++ b/attitude/complementary.go
@@ -6,43 +6,46 @@ import (
 	"time"
 )
 
+const rad2Deg = 180 / math.Pi
+
+// NewComplementary returns a new Complementary filter.
 func NewComplementary() *Complementary {
 	return &Complementary{gGain: 0.98, aGain: 0.02}
-	//return &Complementary{gGain: 1, aGain: 0}
 
 }
 
+// Implements a simple complementation filter.
+// see http://www.pieter-jan.com/node/11
 type Complementary struct {
-	data    Data
+	state   Attitude
 	updated time.Time
 	aGain   float64
 	gGain   float64
 }
 
-const rad2Deg = 180 / math.Pi
-
-func (c *Complementary) Update(d imu.Data) Data {
+// Update processes the given imu.Data and returns the new Attitude.
+func (c *Complementary) Update(d imu.Data) Attitude {
 	var (
-		a   Data
-		now = time.Now()
+		accel Attitude
+		now   = time.Now()
 	)
 
-	a.Pitch = angle(d.Ax, d.Az)
-	a.Roll = angle(d.Ay, d.Az)
+	accel.Pitch = angle(d.Ax, d.Az)
+	accel.Roll = angle(d.Ay, d.Az)
 
 	if !c.updated.IsZero() {
 		dt := now.Sub(c.updated).Seconds()
-		c.data.Roll += d.Gx * dt
-		c.data.Pitch += d.Gy * dt
-		c.data.Yaw += d.Gz * dt
+		c.state.Roll += d.Gx * dt
+		c.state.Pitch += d.Gy * dt
+		c.state.Yaw += d.Gz * dt
 	}
 
-	c.data.Pitch = c.data.Pitch*c.gGain + a.Pitch*c.aGain
-	c.data.Roll = c.data.Roll*c.gGain + a.Roll*c.aGain
-	c.data.Altitude = d.UsAltitude
+	c.state.Pitch = c.state.Pitch*c.gGain + accel.Pitch*c.aGain
+	c.state.Roll = c.state.Roll*c.gGain + accel.Roll*c.aGain
+	c.state.Altitude = d.UsAltitude
 
 	c.updated = now
-	return c.data
+	return c.state
 }
 
 func angle(a, b float64) float64 {
diff --git a/attitude/doc.go b/attitude/doc.go
new file mode 100644
index 0000000..800e059
--- /dev/null
+++ b/attitude/doc.go
@@ -0,0 +1,3 @@
+// Package attitude contains algorithm for determining the drones position
+// relative to the ground.
+package attitude
diff --git a/control/control.go b/control/control.go
index 70c69a9..d9226ed 100644
--- a/control/control.go
+++ b/control/control.go
@@ -30,7 +30,7 @@ type Control struct {
 	throttle float64
 }
 
-func (c *Control) Set(s attitude.Data, throttle float64) {
+func (c *Control) Set(s attitude.Attitude, throttle float64) {
 	c.l.Lock()
 	defer c.l.Unlock()
 
@@ -40,7 +40,7 @@ func (c *Control) Set(s attitude.Data, throttle float64) {
 	c.throttle = throttle
 }
 
-func (c *Control) Update(a attitude.Data) (speeds [4]float64) {
+func (c *Control) Update(a attitude.Attitude) (speeds [4]float64) {
 	c.l.Lock()
 	defer c.l.Unlock()
 
diff --git a/http/handler.go b/http/handler.go
index 329e04e..3d018cc 100644
--- a/http/handler.go
+++ b/http/handler.go
@@ -26,11 +26,11 @@ type Handler struct {
 
 type update struct {
 	NavData      navboard.Data
-	AttitudeData attitude.Data
+	AttitudeData attitude.Attitude
 }
 
 type setpoint struct {
-	attitude.Data
+	attitude.Attitude
 	Throttle float64
 }
 
@@ -78,7 +78,7 @@ func (h *Handler) handleWebsocket(conn *websocket.Conn) {
 				return
 			}
 		case s := <-setCh:
-			h.config.Control.Set(s.Data, s.Throttle)
+			h.config.Control.Set(s.Attitude, s.Throttle)
 		case err := <-setErrCh:
 			log.Warn("WebSocket error. err=%s ip=%s", err, ip)
 			return
@@ -94,7 +94,7 @@ func (h *Handler) ServeHTTP(w http.ResponseWriter, r *http.Request) {
 	h.fileHandler.ServeHTTP(w, r)
 }
 
-func (h *Handler) Update(n navboard.Data, a attitude.Data) {
+func (h *Handler) Update(n navboard.Data, a attitude.Attitude) {
 	h.pub(update{n, a})
 }