diff --git a/companion/src/eeprominterface.h b/companion/src/eeprominterface.h
index 4cde2ced6..13554eb9a 100644
--- a/companion/src/eeprominterface.h
+++ b/companion/src/eeprominterface.h
@@ -956,7 +956,7 @@ class SensorData {
     unsigned int index;
 
     // for calculations
-    unsigned int sources[4];
+    int sources[4];
 
     // for GPS dist
     unsigned int gps;
diff --git a/companion/src/firmwares/opentx/opentxeeprom.cpp b/companion/src/firmwares/opentx/opentxeeprom.cpp
index e10ce2173..84f3555c3 100644
--- a/companion/src/firmwares/opentx/opentxeeprom.cpp
+++ b/companion/src/firmwares/opentx/opentxeeprom.cpp
@@ -2671,7 +2671,7 @@ class SensorField: public TransformedField {
         if (sensor.formula == SensorData::FORMULA_CELL)
           _param = (sensor.source) + (sensor.index << 8);
         else if (sensor.formula == SensorData::FORMULA_ADD || sensor.formula == SensorData::FORMULA_MULTIPLY || sensor.formula == SensorData::FORMULA_MIN || sensor.formula == SensorData::FORMULA_MAX)
-          _param = (sensor.sources[0]) + (sensor.sources[1] << 8) + (sensor.sources[2] << 16) + (sensor.sources[3] << 24);
+          _param = ((uint8_t)sensor.sources[0]) + ((uint8_t)sensor.sources[1] << 8) + ((uint8_t)sensor.sources[2] << 16) + ((uint8_t)sensor.sources[3] << 24);
         else if (sensor.formula == SensorData::FORMULA_DIST)
           _param = (sensor.gps) + (sensor.alt << 8);
         else if (sensor.formula == SensorData::FORMULA_CONSUMPTION)
diff --git a/companion/src/modeledit/telemetry.cpp b/companion/src/modeledit/telemetry.cpp
index 78f0fb858..daa655d5a 100644
--- a/companion/src/modeledit/telemetry.cpp
+++ b/companion/src/modeledit/telemetry.cpp
@@ -488,6 +488,12 @@ TelemetrySensorPanel::TelemetrySensorPanel(QWidget *parent, SensorData & sensor,
   ui->altSensor->setField(sensor.alt);
   ui->ampsSensor->setField(sensor.amps);
   ui->cellsSensor->setField(sensor.source);
+  ui->cellsIndex->addItem(tr("Lowest"), 0);
+  for (int i=1; i<=6; ++i)
+    ui->cellsIndex->addItem(tr("Cell %1").arg(i), i);
+  ui->cellsIndex->addItem(tr("Highest"), 0);
+  ui->cellsIndex->addItem(tr("Delta"), 0);
+  ui->cellsIndex->setField(sensor.index);
   ui->source1->setField(sensor.sources[0]);
   ui->source2->setField(sensor.sources[1]);
   ui->source3->setField(sensor.sources[2]);
@@ -530,13 +536,14 @@ void TelemetrySensorPanel::update()
     consFieldsDisplayed = (sensor.formula == SensorData::FORMULA_CONSUMPTION);
     sources12FieldsDisplayed = (sensor.formula <= SensorData::FORMULA_MULTIPLY);
     sources34FieldsDisplayed = (sensor.formula < SensorData::FORMULA_MULTIPLY);
-    updateSourcesComboBox(ui->source1);
-    updateSourcesComboBox(ui->source2);
-    updateSourcesComboBox(ui->source3);
-    updateSourcesComboBox(ui->source4);
-    updateSourcesComboBox(ui->gpsSensor);
-    updateSourcesComboBox(ui->altSensor);
-    updateSourcesComboBox(ui->ampsSensor);
+    updateSourcesComboBox(ui->source1, true);
+    updateSourcesComboBox(ui->source2, true);
+    updateSourcesComboBox(ui->source3, true);
+    updateSourcesComboBox(ui->source4, true);
+    updateSourcesComboBox(ui->gpsSensor, false);
+    updateSourcesComboBox(ui->altSensor, false);
+    updateSourcesComboBox(ui->ampsSensor, false);
+    updateSourcesComboBox(ui->cellsSensor, false);
   }
   else {
     ui->idLabel->show();
@@ -573,19 +580,25 @@ void TelemetrySensorPanel::update()
   lock = false;
 }
 
-void populateTelemetrySourcesComboBox(AutoComboBox * cb, const ModelData * model)
+void populateTelemetrySourcesComboBox(AutoComboBox * cb, const ModelData * model, bool negative)
 {
   cb->clear();
+  if (negative) {
+    for (int i=-C9X_MAX_SENSORS; i<0; ++i) {
+      if (model->sensorData[-i-1].isAvailable())
+        cb->addItem(QObject::tr("-%1").arg(model->sensorData[-i-1].label), i);
+    }
+  }
   cb->addItem("---", 0);
-  for (int i=0; i<C9X_MAX_SENSORS; ++i) {
-    if (model->sensorData[i].isAvailable())
-      cb->addItem(model->sensorData[i].label, i+1);
+  for (int i=1; i<=C9X_MAX_SENSORS; ++i) {
+    if (model->sensorData[i-1].isAvailable())
+      cb->addItem(model->sensorData[i-1].label, i);
   }
 }
 
-void TelemetrySensorPanel::updateSourcesComboBox(AutoComboBox * cb)
+void TelemetrySensorPanel::updateSourcesComboBox(AutoComboBox * cb, bool negative)
 {
-  populateTelemetrySourcesComboBox(cb, model);
+  populateTelemetrySourcesComboBox(cb, model, negative);
 }
 
 void TelemetrySensorPanel::on_name_editingFinished()
@@ -712,8 +725,8 @@ void TelemetryPanel::update()
       ui->telemetryProtocol->setCurrentIndex(0);
     }
 
-    populateTelemetrySourcesComboBox(ui->voltsSource, model);
-    populateTelemetrySourcesComboBox(ui->altitudeSource, model);
+    populateTelemetrySourcesComboBox(ui->voltsSource, model, false);
+    populateTelemetrySourcesComboBox(ui->altitudeSource, model, false);
   }
 
   if (IS_ARM(firmware->getBoard())) {
diff --git a/companion/src/modeledit/telemetry.h b/companion/src/modeledit/telemetry.h
index c9ef61591..cd5797872 100644
--- a/companion/src/modeledit/telemetry.h
+++ b/companion/src/modeledit/telemetry.h
@@ -95,7 +95,7 @@ class TelemetrySensorPanel: public ModelPanel
     void on_prec_editingFinished();
 
   protected:
-    void updateSourcesComboBox(AutoComboBox * cb);
+    void updateSourcesComboBox(AutoComboBox * cb, bool negative);
 
   private:
     Ui::TelemetrySensor * ui;
diff --git a/companion/src/shared/autocombobox.h b/companion/src/shared/autocombobox.h
index f5c9db044..ad370d83b 100755
--- a/companion/src/shared/autocombobox.h
+++ b/companion/src/shared/autocombobox.h
@@ -25,7 +25,7 @@ class AutoComboBox: public QComboBox
       lock = false;
     }
 
-    void addItem(const QString & item, unsigned int value)
+    void addItem(const QString & item, int value)
     {
       lock = true;
       QComboBox::addItem(item, value);
@@ -36,6 +36,17 @@ class AutoComboBox: public QComboBox
     }
 
     void setField(unsigned int & field, ModelPanel * panel=NULL)
+    {
+      this->field = (int *)&field;
+      this->panel = panel;
+      for (int i=0; i<count(); ++i) {
+        setItemData(i, i);
+        if ((int)field == i)
+          setCurrentIndex(i);
+      }
+    }
+
+    void setField(int & field, ModelPanel * panel=NULL)
     {
       this->field = &field;
       this->panel = panel;
@@ -58,7 +69,7 @@ class AutoComboBox: public QComboBox
     }
 
   protected:
-    unsigned int * field;
+    int * field;
     ModelPanel * panel;
     bool lock;
 };
diff --git a/radio/src/gui/menu_model.cpp b/radio/src/gui/menu_model.cpp
index 74615303f..5288efcf7 100644
--- a/radio/src/gui/menu_model.cpp
+++ b/radio/src/gui/menu_model.cpp
@@ -5886,10 +5886,8 @@ bool isSensorAvailable(int sensor)
 {
   if (sensor == 0)
     return true;
-
-  sensor -= 1;
-
-  return isTelemetryFieldAvailable(sensor);
+  else
+    return isTelemetryFieldAvailable(abs(sensor) - 1);
 }
 
 #define SENSOR_2ND_COLUMN (12*FW)
@@ -6038,7 +6036,7 @@ void menuModelSensor(uint8_t event)
       case SENSOR_FIELD_PARAM2:
         if (sensor->type == TELEM_TYPE_CALCULATED) {
           if (sensor->formula == TELEM_FORMULA_CELL) {
-            sensor->cell.index = selectMenuItem(SENSOR_2ND_COLUMN, y, "Cell index", "\007Lowest\0001\0     2\0     3\0     4\0     5\0     6\0     Highest", sensor->cell.index, 0, 7, attr, event);
+            sensor->cell.index = selectMenuItem(SENSOR_2ND_COLUMN, y, "Cell index", "\007Lowest\0001\0     2\0     3\0     4\0     5\0     6\0     HighestDelta\0", sensor->cell.index, 0, 8, attr, event);
             break;
           }
           else if (sensor->formula == TELEM_FORMULA_DIST) {
@@ -6065,10 +6063,16 @@ void menuModelSensor(uint8_t event)
       case SENSOR_FIELD_PARAM4:
       {
         putsStrIdx(0, y, "Source", k-SENSOR_FIELD_PARAM1+1);
-        uint8_t & source = sensor->calc.sources[k-SENSOR_FIELD_PARAM1];
-        putsMixerSource(SENSOR_2ND_COLUMN, y, source ? MIXSRC_FIRST_TELEM+3*(source-1) : 0, attr);
+        int8_t & source = sensor->calc.sources[k-SENSOR_FIELD_PARAM1];
         if (attr) {
-          source = checkIncDec(event, source, 0, TELEM_VALUES_MAX, EE_MODEL|NO_INCDEC_MARKS, isSensorAvailable);
+          source = checkIncDec(event, source, -TELEM_VALUES_MAX, TELEM_VALUES_MAX, EE_MODEL|NO_INCDEC_MARKS, isSensorAvailable);
+        }
+        if (source < 0) {
+          lcd_putcAtt(SENSOR_2ND_COLUMN, y, '-', attr);
+          putsMixerSource(lcdNextPos, y, MIXSRC_FIRST_TELEM+3*(-1-source), attr);
+        }
+        else {
+          putsMixerSource(SENSOR_2ND_COLUMN, y, source ? MIXSRC_FIRST_TELEM+3*(source-1) : 0, attr);
         }
         break;
       }
diff --git a/radio/src/myeeprom.h b/radio/src/myeeprom.h
index b0d177563..c24807899 100644
--- a/radio/src/myeeprom.h
+++ b/radio/src/myeeprom.h
@@ -1181,7 +1181,7 @@ PACK(typedef struct {
       uint16_t spare;
     }) cell;
     PACK(struct {
-      uint8_t sources[4];
+      int8_t sources[4];
     }) calc;
     PACK(struct {
       uint8_t source;
diff --git a/radio/src/telemetry/telemetry.cpp b/radio/src/telemetry/telemetry.cpp
index 765ece464..a9c53eb94 100755
--- a/radio/src/telemetry/telemetry.cpp
+++ b/radio/src/telemetry/telemetry.cpp
@@ -242,25 +242,39 @@ void TelemetryItem::eval(const TelemetrySensor & sensor)
           lastReceived = TELEMETRY_VALUE_OLD;
         }
         else {
-          uint8_t index = sensor.cell.index;
-          if (index == 0 || index == 7) {
-            bool lowest = (index == 0);
-            index = 0;
+          unsigned int index = sensor.cell.index;
+          if (index == TELEM_CELL_INDEX_LOWEST || index == TELEM_CELL_INDEX_HIGHEST || index == TELEM_CELL_INDEX_DELTA) {
+            unsigned int lowest=0, highest=0;
             for (int i=0; i<cellsItem.cells.count; i++) {
               if (cellsItem.cells.values[i].state) {
-                if (index == 0 || (lowest && cellsItem.cells.values[i].value < cellsItem.cells.values[index-1].value) || (!lowest && cellsItem.cells.values[i].value > cellsItem.cells.values[index-1].value)) {
-                  index = i+1;
-                }
+                if (!lowest || cellsItem.cells.values[i].value < cellsItem.cells.values[lowest-1].value)
+                  lowest = i+1;
+                if (!highest || cellsItem.cells.values[i].value > cellsItem.cells.values[highest-1].value)
+                  highest = i+1;
               }
               else {
-                index = 0;
-                break;
+                lowest = highest = 0;
+              }
+            }
+            if (lowest) {
+              switch (index) {
+                case TELEM_CELL_INDEX_LOWEST:
+                  setValue(sensor, cellsItem.cells.values[lowest-1].value, UNIT_VOLTS, 2);
+                  break;
+                case TELEM_CELL_INDEX_HIGHEST:
+                  setValue(sensor, cellsItem.cells.values[highest-1].value, UNIT_VOLTS, 2);
+                  break;
+                case TELEM_CELL_INDEX_DELTA:
+                  setValue(sensor, cellsItem.cells.values[highest-1].value - cellsItem.cells.values[lowest-1].value, UNIT_VOLTS, 2);
+                  break;
               }
             }
           }
-          index -= 1;
-          if (index < cellsItem.cells.count && cellsItem.cells.values[index].state) {
-            setValue(sensor, cellsItem.cells.values[index].value, UNIT_VOLTS, 2);
+          else {
+            index -= 1;
+            if (index < cellsItem.cells.count && cellsItem.cells.values[index].state) {
+              setValue(sensor, cellsItem.cells.values[index].value, UNIT_VOLTS, 2);
+            }
           }
         }
       }
@@ -322,10 +336,11 @@ void TelemetryItem::eval(const TelemetrySensor & sensor)
         value = 1;
       }
       for (int i=0; i<maxitems; i++) {
-        uint8_t source = sensor.calc.sources[i];
+        int8_t source = sensor.calc.sources[i];
         if (source) {
-          TelemetrySensor & telemetrySensor = g_model.telemetrySensors[source-1];
-          TelemetryItem & telemetryItem = telemetryItems[source-1];
+          unsigned int index = abs(source)-1;
+          TelemetrySensor & telemetrySensor = g_model.telemetrySensors[index];
+          TelemetryItem & telemetryItem = telemetryItems[index];
           if (sensor.formula == TELEM_FORMULA_AVERAGE) {
             if (telemetryItem.isAvailable())
               available = 1;
@@ -343,13 +358,16 @@ void TelemetryItem::eval(const TelemetrySensor & sensor)
               return;
             }
           }
+          int32_t sensorValue = telemetryItem.value;
+          if (source < 0)
+            sensorValue = -sensorValue;
           count += 1;
           if (sensor.formula == TELEM_FORMULA_MULTIPLY) {
             mulprec += telemetrySensor.prec;
-            value *= convertTelemetryValue(telemetryItem.value, telemetrySensor.unit, 0, sensor.unit, 0);
+            value *= convertTelemetryValue(sensorValue, telemetrySensor.unit, 0, sensor.unit, 0);
           }
           else {
-            int32_t sensorValue = convertTelemetryValue(telemetryItem.value, telemetrySensor.unit, telemetrySensor.prec, sensor.unit, sensor.prec);
+            sensorValue = convertTelemetryValue(sensorValue, telemetrySensor.unit, telemetrySensor.prec, sensor.unit, sensor.prec);
             if (sensor.formula == TELEM_FORMULA_MIN)
               value = (count==1 ? sensorValue : min<int32_t>(value, sensorValue));
             else if (sensor.formula == TELEM_FORMULA_MAX)
diff --git a/radio/src/telemetry/telemetry.h b/radio/src/telemetry/telemetry.h
index a5d667d14..e328811f5 100755
--- a/radio/src/telemetry/telemetry.h
+++ b/radio/src/telemetry/telemetry.h
@@ -50,6 +50,18 @@ enum TelemetryProtocol
 
 #define TELEMETRY_AVERAGE_COUNT       3
 
+enum {
+  TELEM_CELL_INDEX_LOWEST,
+  TELEM_CELL_INDEX_1,
+  TELEM_CELL_INDEX_2,
+  TELEM_CELL_INDEX_3,
+  TELEM_CELL_INDEX_4,
+  TELEM_CELL_INDEX_5,
+  TELEM_CELL_INDEX_6,
+  TELEM_CELL_INDEX_HIGHEST,
+  TELEM_CELL_INDEX_DELTA,
+};
+
 PACK(struct CellValue
 {
   uint16_t value:15;