diff --git a/include/xo/unit/mpl/dim_util.hpp b/include/xo/unit/mpl/dim_util.hpp
new file mode 100644
index 00000000..7d369bc2
--- /dev/null
+++ b/include/xo/unit/mpl/dim_util.hpp
@@ -0,0 +1,82 @@
+/* @file dim_util.hpp */
+
+#pragma once
+
+//#include "stringliteral.hpp"
+//#include "xo/flatstring/flatstring.hpp"
+#include <cstdint>
+
+namespace xo {
+    namespace unit {
+        enum class dim {
+            invalid = -1,
+
+            /** weight.  native unit = 1 gram **/
+            mass,
+            /** distance.  native unit = 1 meter **/
+            distance,
+            /** time. native unit = 1 second **/
+            time,
+            /** a currency amount. native unit depends on actual currency.
+             *  For USD: one US dollar.
+             *
+             *  NOTE: unit system isn't suitable for multicurrency work:
+             *        (1usd + 1eur) is well-defined,  but (1sec + 1m) is not.
+             **/
+            currency,
+            /** a screen price **/
+            price,
+
+            /** comes last, counts entries **/
+            n_dim
+        };
+
+        inline const char *
+        dim2str(dim x)
+        {
+            switch(x) {
+            case dim::mass: return "mass";
+            case dim::distance: return "distance";
+            case dim::time: return "time";
+            case dim::currency: return "currency";
+            case dim::price: return "price";
+            default: break;
+            }
+            return "?dim";
+        }
+
+        static constexpr std::size_t n_dim = static_cast<std::size_t>(dim::n_dim);
+
+        enum class native_unit_id {
+            gram,
+            meter,
+            second,
+            currency,
+            price
+        };
+
+        template <dim Dim>
+        struct native_unit_for;
+
+        template <>
+        struct native_unit_for<dim::mass> { static constexpr auto value = native_unit_id::gram; };
+
+        template <>
+        struct native_unit_for<dim::distance> { static constexpr auto value = native_unit_id::meter; };
+
+        template <>
+        struct native_unit_for<dim::time> { static constexpr auto value = native_unit_id::second; };
+
+        template <>
+        struct native_unit_for<dim::currency> { static constexpr auto value = native_unit_id::currency; };
+
+        template <>
+        struct native_unit_for<dim::price> { static constexpr auto value = native_unit_id::price; };
+
+        template <dim Dim>
+        constexpr auto native_unit_for_v = native_unit_for<Dim>::value;
+
+    } /*namespace unit*/
+} /*namespace xo*/
+
+/* end dim_util.hpp */
diff --git a/include/xo/unit/mpl/numeric_concept.hpp b/include/xo/unit/mpl/numeric_concept.hpp
new file mode 100644
index 00000000..f1d32f58
--- /dev/null
+++ b/include/xo/unit/mpl/numeric_concept.hpp
@@ -0,0 +1,34 @@
+/* @file numeric_concept.hpp */
+
+#pragma once
+
+#include <concepts>
+
+namespace xo {
+    namespace unit {
+        /** @concept numeric_concept
+         *  @brief Concept for values that participate in arithmetic operations (+,-,*,/) and comparisons
+         *
+         *  Intended to include at least:
+         *  - built-in integral and floating-point types
+         *  - xo::raio<U>
+         *  - xo::unit::quantity<U,R>
+         *
+         *  Intend numeric_concept to apply to types suitable for
+         *  xo::unit::quantity::repr_type.
+         **/
+        template <typename T, typename U = T>
+        concept numeric_concept = requires(T x, U y)
+        {
+            { -x };
+            { x - y };
+            { x + y };
+            { x * y };
+            { x / y };
+            { x == y };
+            { x != y };
+        };
+    } /*namespace unit*/
+} /*namespace xo*/
+
+/* end numeric_concept.hpp */