diff --git a/src/units.hh b/src/units.hh
index 652b66ab..8f9172ca 100644
--- a/src/units.hh
+++ b/src/units.hh
@@ -17,28 +17,28 @@ public:
                      "RealType is not derived from StronglyTypedNumber");
     }
 
-    constexpr RealType operator+(const RealType& other) const
+    constexpr RealType operator+(RealType other) const
     { return RealType(m_value + other.m_value); }
 
-    constexpr RealType operator-(const RealType& other) const
+    constexpr RealType operator-(RealType other) const
     { return RealType(m_value - other.m_value); }
 
-    constexpr RealType operator*(const RealType& other) const
+    constexpr RealType operator*(RealType other) const
     { return RealType(m_value * other.m_value); }
 
-    constexpr RealType operator/(const RealType& other) const
+    constexpr RealType operator/(RealType other) const
     { return RealType(m_value / other.m_value); }
 
-    RealType& operator+=(const RealType& other)
+    RealType& operator+=(RealType other)
     { m_value += other.m_value; return static_cast<RealType&>(*this); }
 
-    RealType& operator-=(const RealType& other)
+    RealType& operator-=(RealType other)
     { m_value -= other.m_value; return static_cast<RealType&>(*this); }
 
-    RealType& operator*=(const RealType& other)
+    RealType& operator*=(RealType other)
     { m_value *= other.m_value; return static_cast<RealType&>(*this); }
 
-    RealType& operator/=(const RealType& other)
+    RealType& operator/=(RealType other)
     { m_value /= other.m_value; return static_cast<RealType&>(*this); }
 
     RealType& operator++()
@@ -55,22 +55,22 @@ public:
 
     constexpr RealType operator-() { return RealType(-m_value); }
 
-    constexpr bool operator==(const RealType& other) const
+    constexpr bool operator==(RealType other) const
     { return m_value == other.m_value; }
 
-    constexpr bool operator!=(const RealType& other) const
+    constexpr bool operator!=(RealType other) const
     { return m_value != other.m_value; }
 
-    constexpr bool operator<(const RealType& other) const
+    constexpr bool operator<(RealType other) const
     { return m_value < other.m_value; }
 
-    constexpr bool operator<=(const RealType& other) const
+    constexpr bool operator<=(RealType other) const
     { return m_value <= other.m_value; }
 
-    constexpr bool operator>(const RealType& other) const
+    constexpr bool operator>(RealType other) const
     { return m_value > other.m_value; }
 
-    constexpr bool operator>=(const RealType& other) const
+    constexpr bool operator>=(RealType other) const
     { return m_value >= other.m_value; }
 
     constexpr bool operator!() const