diff --git a/lib/ServiceDelegate/History.js b/lib/ServiceDelegate/History.js
index 433d6f7..e1042af 100644
--- a/lib/ServiceDelegate/History.js
+++ b/lib/ServiceDelegate/History.js
@@ -76,7 +76,7 @@ class HistoryValue {
     * @params {Buffer} buffer - The buffer to write to.
     * @params {integer} offset - The offset within the buffer.
     */
-  writeEntry (entry, buffer, offset) { buffer.writeUInt16LE(entry[this.id], offset) }
+  writeEntry (entry, buffer, offset) { buffer.writeInt16LE(entry[this.id], offset) }
 }
 
 class TemperatureValue extends HistoryValue {
@@ -133,69 +133,97 @@ class ContactValue extends HistoryValue {
   }
 }
 
+// Device delivers consumption in kWh.
 class ConsumptionValue extends HistoryValue {
   get tag () { return 0x07 }
   get id () { return 'p' }
 
   constructor (parent, delegate) {
     super(parent, delegate)
-    this._consumption = delegate.value
+    this._consumption = delegate.value // kWh
     this._time = History.now()
   }
 
   prepareEntry (entry) {
-    const delta = this._delegate.value - this._consumption // kWh
-    const period = entry.time - this._time // s
-    const power = period === 0 ? 0 : 1000 * 3600 * delta / period // W
+    let delta = this._delegate.value - this._consumption // kWh
+    delta *= 1000 // Wh
+    entry[this.id] = Math.round(delta * 10) // 0.1 Wh
     if (this._parent.computedPowerDelegate != null) {
+      // Optionally compute (average) power.
+      delta *= 3600 // Ws
+      const period = entry.time - this._time // s
+      const power = period === 0 ? 0 : delta / period // W
       this._parent.computedPowerDelegate.value = Math.round(power) // W
     }
-    entry[this.id] = Math.round(power * 10) // 0.1 W * 10 min
-    this._consumption = this._delegate.value
+    this._consumption -= this._delegate.value
     this._time = entry.time
   }
 }
 
+// Device delivers power in W.
 class PowerValue extends HistoryValue {
   get tag () { return 0x07 }
   get id () { return 'p' }
 
   constructor (parent, delegate) {
     super(parent, delegate)
-    this._runningConsumption = 0 // 10-min-interval running value
-    this._totalConsumption = parent.computedConsumptionDelegate.value * 100
-    this._power = delegate.value // current power
-    this._time = History.now() // start time of current power
+    this._runningConsumption = 0 // Ws
+    this._totalConsumption = parent.computedConsumptionDelegate.value // kWh
+    this._totalConsumption *= 3600 * 1000 // Ws
+    this._power = delegate.value // W
+    this._time = History.now()
     delegate.on('didSet', (value) => {
       const now = History.now()
       const delta = this._power * (now - this._time) // Ws
-      this._runningConsumption += Math.round(delta / 60.0) // 0.1W * 10 min
-      this._totalConsumption += delta / 36000.0 // 0.01 kWh
-      this._power = value
+      this._runningConsumption += delta // Ws
+      this._totalConsumption += delta // Ws
+      this._power = value // W
       this._time = now
     })
     parent.addCharacteristicDelegate({
       key: 'resetTotal',
       Characteristic: parent.Characteristics.eve.ResetTotal
     }).on('didSet', (value) => {
-      this._runningConsumption = 0
-      this._totalConsumption = 0
-      parent.computedConsumptionDelegate.value = this._totalConsumption
+      this._runningConsumption = 0 // Ws
+      this._totalConsumption = 0 // Ws
+      const totalConsumption = this._totalConsumption * 3600 * 1000 * 100 // 0.01 kWh
+      parent.computedConsumptionDelegate.value = Math.round(totalConsumption) / 100.0 // kWh
     })
   }
 
   prepareEntry (entry) {
     const delta = this._power * (entry.time - this._time) // Ws
-    this._runningConsumption += delta / 60.0 // 0.1 W * 10 min
-    this._totalConsumption += delta / 36000.0 // 0.01 kWh
-    this._parent.computedConsumptionDelegate.value = Math.round(this._totalConsumption) / 100.0 // kWh
-    entry[this.id] = Math.round(this._runningConsumption) // 0.1 W * 10 min
+    this._runningConsumption += delta // Ws
+    this._totalConsumption += delta // Ws
+    const consumption = this.this._runningConsumption * 3600 // Wh
+    entry[this.id] = Math.round(consumption * 10) // 0.1 Wh
+    const totalConsumption = this._totalConsumption * 3600 * 1000 * 100 // 0.01 kWh
+    this._parent.computedConsumptionDelegate.value = Math.round(totalConsumption) / 100.0 // kWh
     this._power = this._delegate.value
     this._time = entry.time
     this._runningConsumption = 0
   }
 }
 
+// Device delivers running avarage of power in W.
+class AveragePowerValue extends HistoryValue {
+  get tag () { return 0x07 }
+  get id () { return 'p' }
+
+  constructor (parent, delegate) {
+    super(parent, delegate)
+    this._time = History.now()
+  }
+
+  prepareEntry (entry) {
+    const delta = entry.time - this._time // s
+    let consumption = this._delegate.value * delta // Ws
+    consumption *= 3600 // Wh
+    entry[this.id] = Math.round(consumption * 10) // 0.1 Wh
+    this._time = entry.time
+  }
+}
+
 class SwitchOnValue extends HistoryValue {
   get tag () { return 0x0E }
   get length () { return 1 }
@@ -285,6 +313,7 @@ const historyValueTypes = {
   airPressure: AirPressureValue,
   contact: ContactValue,
   power: PowerValue,
+  averagePower: AveragePowerValue,
   switchOn: SwitchOnValue,
   consumption: ConsumptionValue,
   valvePosition: ValvePositionValue,
@@ -597,12 +626,14 @@ class History extends ServiceDelegate {
     let bitmap = 0
     let offset = 1
     for (const i in this._valueTypes) {
-      const valueType = this._valueTypes[i]
-      if (entry[valueType.id] != null) {
-        bitmap |= 0x01 << i
-        valueType.writeEntry(entry, buffer, offset)
-        offset += valueType.length
-      }
+      try {
+        const valueType = this._valueTypes[i]
+        if (entry[valueType.id] != null) {
+          bitmap |= 0x01 << i
+          valueType.writeEntry(entry, buffer, offset)
+          offset += valueType.length
+        }
+      } catch (error) { this.warn(error) }
     }
     buffer.writeUInt8(bitmap, 0)
     return buffer.slice(0, offset)