diff --git a/src/blackmisc/aviation/aircraftsituationlist.cpp b/src/blackmisc/aviation/aircraftsituationlist.cpp
index 418e94e18..ad6484e42 100644
--- a/src/blackmisc/aviation/aircraftsituationlist.cpp
+++ b/src/blackmisc/aviation/aircraftsituationlist.cpp
@@ -349,13 +349,16 @@ namespace BlackMisc
             return c;
         }
 
-        void CAircraftSituationList::addAltitudeOffset(const CLength &offset)
+        int CAircraftSituationList::addAltitudeOffset(const CLength &offset)
         {
-            if (offset.isNull() || this->isEmpty()) { return; }
+            if (offset.isNull() || this->isEmpty()) { return 0; }
+            int c = 0;
             for (CAircraftSituation &s : *this)
             {
                 s.addAltitudeOffset(offset);
+                c++;
             }
+            return c;
         }
 
         bool CAircraftSituationList::isSortedAdjustedLatestFirstWithoutNullPositions() const
diff --git a/src/blackmisc/aviation/aircraftsituationlist.h b/src/blackmisc/aviation/aircraftsituationlist.h
index 04407d88b..2a3b41252 100644
--- a/src/blackmisc/aviation/aircraftsituationlist.h
+++ b/src/blackmisc/aviation/aircraftsituationlist.h
@@ -132,7 +132,7 @@ namespace BlackMisc
             int setOnGroundDetails(CAircraftSituation::OnGroundDetails details);
 
             //! Add an offset to each altitude
-            void addAltitudeOffset(const PhysicalQuantities::CLength &offset);
+            int addAltitudeOffset(const PhysicalQuantities::CLength &offset);
 
             //! Latest first and no null positions?
             bool isSortedAdjustedLatestFirstWithoutNullPositions() const;
diff --git a/src/blackmisc/aviation/altitude.cpp b/src/blackmisc/aviation/altitude.cpp
index 67756d2b2..39501d12d 100644
--- a/src/blackmisc/aviation/altitude.cpp
+++ b/src/blackmisc/aviation/altitude.cpp
@@ -30,30 +30,32 @@ namespace BlackMisc
 
         CAltitude CAltitude::withOffset(const CLength &offset) const
         {
+            if (this->isNull()) { return CAltitude(offset, CAltitude::MeanSeaLevel); }
             CAltitude copy(*this);
-            if (!offset.isNull() && !offset.isZeroEpsilonConsidered()) { copy += offset; }
+            if (!offset.isNull() && !offset.isZeroEpsilonConsidered())
+            {
+                copy += offset;
+            }
             return copy;
         }
 
+        void CAltitude::addOffset(const CLength &offset)
+        {
+            *this = this->withOffset(offset);
+        }
+
         QString CAltitude::convertToQString(bool i18n) const
         {
             if (this->m_datum == FlightLevel)
             {
+                static const QString fls("FL%1");
                 const int fl = qRound(this->CLength::value(CLengthUnit::ft()) / 100.0);
-                return QString("FL%1").arg(fl);
+                return fls.arg(fl);
             }
             else
             {
-                QString s;
-                if (this->getUnit() == CLengthUnit::m())
-                {
-                    s = this->CLength::valueRoundedWithUnit(1, i18n);
-                }
-                else
-                {
-                    s = this->CLength::valueRoundedWithUnit(CLengthUnit::ft(), 0, i18n);
-                }
-                return s.append(this->isMeanSeaLevel() ? QStringLiteral(" MSL") : QStringLiteral(" AGL"));
+                return this->CLength::valueRoundedWithUnit(1, i18n) %
+                       (this->isMeanSeaLevel() ? QStringLiteral(" MSL") : QStringLiteral(" AGL"));
             }
         }
 
diff --git a/src/blackmisc/aviation/altitude.h b/src/blackmisc/aviation/altitude.h
index f5e9955da..987c9476c 100644
--- a/src/blackmisc/aviation/altitude.h
+++ b/src/blackmisc/aviation/altitude.h
@@ -105,6 +105,9 @@ namespace BlackMisc
             //! \remark epsilon 0 (zero) values ignored
             CAltitude withOffset(const CLength &offset) const;
 
+            //! Add offset value
+            void addOffset(const CLength &offset);
+
             //! AGL Above ground level?
             bool isAboveGroundLevel() const { return AboveGround == this->m_datum; }
 
diff --git a/src/blackmisc/aviation/callsignobjectlist.cpp b/src/blackmisc/aviation/callsignobjectlist.cpp
index 5dadfaaee..b727991ec 100644
--- a/src/blackmisc/aviation/callsignobjectlist.cpp
+++ b/src/blackmisc/aviation/callsignobjectlist.cpp
@@ -215,6 +215,14 @@ namespace BlackMisc
             container().sortBy(&OBJ::getCallsign);
         }
 
+        template<class OBJ, class CONTAINER>
+        CONTAINER ICallsignObjectList<OBJ, CONTAINER>::sortedByCallsign() const
+        {
+            CONTAINER copy(this->container());
+            copy.sortByCallsign();
+            return copy;
+        }
+
         template <class OBJ, class CONTAINER>
         int ICallsignObjectList<OBJ, CONTAINER>::incrementalUpdateOrAdd(const OBJ &objectBeforeChanges, const CPropertyIndexVariantMap &changedValues)
         {
diff --git a/src/blackmisc/aviation/callsignobjectlist.h b/src/blackmisc/aviation/callsignobjectlist.h
index dde42d0c3..2f80f4494 100644
--- a/src/blackmisc/aviation/callsignobjectlist.h
+++ b/src/blackmisc/aviation/callsignobjectlist.h
@@ -104,6 +104,9 @@ namespace BlackMisc
             //! Sort by callsign
             void sortByCallsign();
 
+            //! Copy of list sorted by callsign
+            CONTAINER sortedByCallsign() const;
+
         protected:
             //! Constructor
             ICallsignObjectList();
diff --git a/src/blackmisc/geo/elevationplane.cpp b/src/blackmisc/geo/elevationplane.cpp
index e667adf18..d7be56d41 100644
--- a/src/blackmisc/geo/elevationplane.cpp
+++ b/src/blackmisc/geo/elevationplane.cpp
@@ -38,6 +38,13 @@ namespace BlackMisc
             CCoordinateGeodetic(coordinate), m_radius(radius)
         { }
 
+        void CElevationPlane::addAltitudeOffset(const CLength &offset)
+        {
+            if (offset.isNull() || offset.isZeroEpsilonConsidered()) { return; }
+            const CAltitude newAlt = this->getAltitude().withOffset(offset);
+            this->setGeodeticHeight(newAlt);
+        }
+
         const CAltitude &CElevationPlane::getAltitudeIfWithinRadius(const ICoordinateGeodetic &coordinate) const
         {
             return (isWithinRange(coordinate)) ? geodeticHeight() : CAltitude::null();
diff --git a/src/blackmisc/geo/elevationplane.h b/src/blackmisc/geo/elevationplane.h
index f5ac9d1ba..bfbf9d323 100644
--- a/src/blackmisc/geo/elevationplane.h
+++ b/src/blackmisc/geo/elevationplane.h
@@ -48,6 +48,9 @@ namespace BlackMisc
             //! Radius
             void setRadius(const PhysicalQuantities::CLength &radius) { m_radius = radius; }
 
+            //! Add offset to altitude
+            void addAltitudeOffset(const PhysicalQuantities::CLength &offset);
+
             //! Altitude when within radius, else null
             const Aviation::CAltitude &getAltitudeIfWithinRadius(const ICoordinateGeodetic &coordinate) const;
 
diff --git a/src/blackmisc/pq/physicalquantity.cpp b/src/blackmisc/pq/physicalquantity.cpp
index 0a201347d..0740214f8 100644
--- a/src/blackmisc/pq/physicalquantity.cpp
+++ b/src/blackmisc/pq/physicalquantity.cpp
@@ -143,6 +143,7 @@ namespace BlackMisc
         template <class MU, class PQ>
         const PQ &CPhysicalQuantity<MU, PQ>::makePositive()
         {
+            if (this->isNull() || m_value == 0) { return *this->derived(); }
             if (m_value < 0) { m_value *= -1.0; }
             return *this->derived();
         }
@@ -150,6 +151,7 @@ namespace BlackMisc
         template <class MU, class PQ>
         const PQ &CPhysicalQuantity<MU, PQ>::makeNegative()
         {
+            if (this->isNull() || m_value == 0) { return *this->derived(); }
             if (m_value > 0) { m_value *= -1.0; }
             return *this->derived();
         }
@@ -157,6 +159,7 @@ namespace BlackMisc
         template<class MU, class PQ>
         PQ CPhysicalQuantity<MU, PQ>::abs() const
         {
+            if (this->isNull() || m_value == 0) { return *this->derived(); }
             if (m_value >= 0) { return *this->derived(); }
             PQ copy(*this->derived());
             return copy.makePositive();