diff --git a/src/blackmisc/collection.h b/src/blackmisc/collection.h
index b32b04967..7a7393e8d 100644
--- a/src/blackmisc/collection.h
+++ b/src/blackmisc/collection.h
@@ -22,7 +22,21 @@ namespace BlackMisc
 {
 
     /*!
-     * \brief Generic type-erased unsequenced container with value semantics.
+     * Needed for compatibility with C++ standard algorithms which expect ordered sets.
+     */
+    template <class T>
+    class QOrderedSet : public QMap<T, T>
+    {
+    public:
+        //! Type of values stored in the set.
+        typedef T value_type;
+
+        //! Insert a new value into the set.
+        typename QMap<T, T>::iterator insert(const T &value) { return QMap<T, T>::insert(value, value); }
+    };
+
+    /*!
+     * \brief Generic type-erased ordered container with value semantics.
      * \tparam T the type of elements contained.
      *
      * Can take any suitable container class as its implementation at runtime.
@@ -48,7 +62,7 @@ namespace BlackMisc
         /*!
          * \brief Default constructor.
          */
-        CCollection() : m_pimpl(new Pimpl<QSet<T>>(QSet<T>())) {}
+        CCollection() : m_pimpl(new Pimpl<QOrderedSet<T>>(QOrderedSet<T>())) {}
 
         /*!
          * \brief Copy constructor.
@@ -286,7 +300,7 @@ namespace BlackMisc
             bool operator ==(const PimplBase &other) const override { Pimpl copy = C(); for (auto i = other.cbegin(); i != other.cend(); ++i) copy.insert(*i); return m_impl == copy.m_impl; }
         private:
             C m_impl;
-            // insertHelper: QSet::insert returns an iterator, but std::set::insert returns a std::pair<interator, bool>
+            // insertHelper: QOrderedSet::insert returns an iterator, but std::set::insert returns a std::pair<interator, bool>
             template <class I> static I insertHelper(I i) { return i; }
             template <class I> static I insertHelper(std::pair<I, bool> p) { return p.first; }
         };
@@ -307,6 +321,6 @@ Q_DECLARE_METATYPE(BlackMisc::CCollection<int>)
 Q_DECLARE_METATYPE(BlackMisc::CCollection<uint>)
 Q_DECLARE_METATYPE(BlackMisc::CCollection<qlonglong>)
 Q_DECLARE_METATYPE(BlackMisc::CCollection<qulonglong>)
-// CCollection<double> not instantiated because QSet<double> is not supported due to hashing constraints
+// CCollection<double> not instantiated due to it being a dumb idea because of rounding issues
 
 #endif // guard
diff --git a/src/blackmisc/valueobject.h b/src/blackmisc/valueobject.h
index f5fe4c4b8..177f2b7c9 100644
--- a/src/blackmisc/valueobject.h
+++ b/src/blackmisc/valueobject.h
@@ -21,6 +21,25 @@ namespace BlackMisc
     // forward declaration
     class CIndexVariantMap;
 
+    namespace PhysicalQuantities
+    {
+        template <class MU, class PQ> class CPhysicalQuantity; // forward declaration
+
+        //! Traits class to test whether a class is a physical quantity class. Useful for enable_if.
+        template <class T>
+        class IsQuantity
+        {
+            struct yes { char x; };
+            struct no { yes x[2]; };
+            template <class MU, class PQ> static yes test(const CPhysicalQuantity<MU, PQ> &);
+            static no test(...);
+
+        public:
+            //! True if and only if T is derived from CPhysicalQuantity.
+            static const bool value = sizeof(test(*(T*)0)) == sizeof(yes);
+        };
+    }
+
     /*!
      * \brief Base class for value objects.
      * Public non-virtual interface with protected virtual implementation.
@@ -81,6 +100,42 @@ namespace BlackMisc
         //! Operator != with value map
         friend bool operator!=(const CValueObject &valueObject, const CIndexVariantMap &valueMap);
 
+        //! Comparison operator to allow valueobjects be used as keys in QMap and std::set.
+        template <class T> friend typename std::enable_if<std::is_base_of<CValueObject, T>::value && ! PhysicalQuantities::IsQuantity<T>::value, bool>::type
+        operator<(const T &lhs, const T &rhs)
+        {
+            const auto &lhsBase = static_cast<const CValueObject &>(lhs);
+            const auto &rhsBase = static_cast<const CValueObject &>(rhs);
+            return lhsBase.compareImpl(rhsBase) < 0;
+        }
+
+        //! Comparison for symmetry with operator<.
+        template <class T> friend typename std::enable_if<std::is_base_of<CValueObject, T>::value && ! PhysicalQuantities::IsQuantity<T>::value, bool>::type
+        operator>(const T &lhs, const T &rhs)
+        {
+            const auto &lhsBase = static_cast<const CValueObject &>(lhs);
+            const auto &rhsBase = static_cast<const CValueObject &>(rhs);
+            return lhsBase.compareImpl(rhsBase) > 0;
+        }
+
+        //! Comparison for symmetry with operator<.
+        template <class T> friend typename std::enable_if<std::is_base_of<CValueObject, T>::value && ! PhysicalQuantities::IsQuantity<T>::value, bool>::type
+        operator<=(const T &lhs, const T &rhs)
+        {
+            const auto &lhsBase = static_cast<const CValueObject &>(lhs);
+            const auto &rhsBase = static_cast<const CValueObject &>(rhs);
+            return lhsBase.compareImpl(rhsBase) <= 0;
+        }
+
+        //! Comparison for symmetry with operator<.
+        template <class T> friend typename std::enable_if<std::is_base_of<CValueObject, T>::value && ! PhysicalQuantities::IsQuantity<T>::value, bool>::type
+        operator>=(const T &lhs, const T &rhs)
+        {
+            const auto &lhsBase = static_cast<const CValueObject &>(lhs);
+            const auto &rhsBase = static_cast<const CValueObject &>(rhs);
+            return lhsBase.compareImpl(rhsBase) >= 0;
+        }
+
         /*!
          * Compares two instances of related classes
          * and returns an integer less than, equal to, or greater than zero