diff --git a/docs/install.rst b/docs/install.rst
index 049efc8b..ded68291 100644
--- a/docs/install.rst
+++ b/docs/install.rst
@@ -65,11 +65,7 @@ Installing from source
 ----------------------
 
 Install scripts for `xo-unit`, `xo-ratio` and `xo-flatstring` depend on shared cmake macros
-and a bootstrap script `xo-cmake-config`.
-
-* `xo-cmake`_ source
-
-.. _xo-cmake: https://github.com/rconybea/xo-cmake
+and a bootstrap script `xo-cmake-config` fro `xo-cmake`.
 
 Preamble:
 
diff --git a/include/xo/unit/quantity.hpp b/include/xo/unit/quantity.hpp
index 2691e239..e145db16 100644
--- a/include/xo/unit/quantity.hpp
+++ b/include/xo/unit/quantity.hpp
@@ -264,8 +264,23 @@ namespace xo {
                 return *this;
             }
 
-            // operator*=
-            // operator/=
+            /** multiply @p y in-place.  y must be dimensionless **/
+            template <typename Dimensionless>
+            requires std::is_arithmetic_v<Dimensionless>
+            constexpr
+            quantity & operator*=(Dimensionless y) {
+                this->scale_ *= y;
+                return *this;
+            }
+
+            /** divide @p y in-place.  y must be dimensionless **/
+            template <typename Dimensionless>
+            requires std::is_arithmetic_v<Dimensionless>
+            constexpr
+            quantity & operator/=(Dimensionless y) {
+                this->scale_ /= y;
+                return *this;
+            }
 
             ///@}
 
@@ -634,6 +649,40 @@ namespace xo {
             return detail::quantity_util::subtract(x, y);
         }
 
+        /** subtract an arithmetic value from a dimensionless quantity **/
+        template <typename Quantity,
+                  typename Dimensionless>
+        requires (quantity_concept<Quantity>
+                  && Quantity::is_dimensionless()
+                  && std::is_arithmetic_v<Dimensionless>)
+        constexpr auto
+        operator- (const Quantity & x, Dimensionless y)
+        {
+            using repr_type = std::common_type_t<typename Quantity::repr_type, Dimensionless>;
+
+            auto xp = static_cast<repr_type>(x.scale());
+            auto yp = static_cast<repr_type>(y);
+
+            return xp - yp;
+        }
+
+        /** subtract a dimensionless quantity from an arithmetic value **/
+        template <typename Dimensionless,
+                  typename Quantity>
+        requires (std::is_arithmetic_v<Dimensionless>
+                  && quantity_concept<Quantity>
+                  && Quantity::is_dimensionless())
+        constexpr auto
+        operator- (Dimensionless x, const Quantity & y)
+        {
+            using repr_type = std::common_type_t<Dimensionless, typename Quantity::repr_type>;
+
+            auto xp = static_cast<repr_type>(x);
+            auto yp = static_cast<repr_type>(y.scale());
+
+            return xp - yp;
+        }
+
         ///@}
 
         namespace qty {
diff --git a/include/xo/unit/quantity_ops.hpp b/include/xo/unit/quantity_ops.hpp
index 8f134028..28465be9 100644
--- a/include/xo/unit/quantity_ops.hpp
+++ b/include/xo/unit/quantity_ops.hpp
@@ -9,45 +9,6 @@
 
 namespace xo {
     namespace qty {
-        /** @defgroup quantity-dimensionless-operators **/
-        ///@{
-
-        /** subtract an arithmetic value from a dimensionless quantity **/
-        template <typename Quantity,
-                  typename Dimensionless>
-        requires (quantity_concept<Quantity>
-                  && Quantity::is_dimensionless()
-                  && std::is_arithmetic_v<Dimensionless>)
-        constexpr auto
-        operator- (const Quantity & x, Dimensionless y)
-        {
-            using repr_type = std::common_type_t<typename Quantity::repr_type, Dimensionless>;
-
-            auto xp = static_cast<repr_type>(x.scale());
-            auto yp = static_cast<repr_type>(y);
-
-            return xp - yp;
-        }
-
-        /** subtract a dimensionless quantity from an arithmetic value **/
-        template <typename Dimensionless,
-                  typename Quantity>
-        requires (std::is_arithmetic_v<Dimensionless>
-                  && quantity_concept<Quantity>
-                  && Quantity::is_dimensionless())
-        constexpr auto
-        operator- (Dimensionless x, const Quantity & y)
-        {
-            using repr_type = std::common_type_t<Dimensionless, typename Quantity::repr_type>;
-
-            auto xp = static_cast<repr_type>(x);
-            auto yp = static_cast<repr_type>(y.scale());
-
-            return xp - yp;
-        }
-
-        ///@}
-
         /** note: won't have constexpr result until c++26 (when ::sqrt(), ::pow() are constexpr)
          **/
         template <typename Quantity, typename Quantity2>