diff --git a/src/systems/iec80000/include/mp_units/systems/iec80000/quantities.h b/src/systems/iec80000/include/mp_units/systems/iec80000/quantities.h
index 8af564ee..d28b8e85 100644
--- a/src/systems/iec80000/include/mp_units/systems/iec80000/quantities.h
+++ b/src/systems/iec80000/include/mp_units/systems/iec80000/quantities.h
@@ -29,11 +29,12 @@
 
 namespace mp_units::iec80000 {
 
+// dimensions of base quantities
 // clang-format off
 inline constexpr struct dim_traffic_intensity : base_dimension<"A"> {} dim_traffic_intensity;
-inline constexpr struct dim_storage_capacity : base_dimension<"M"> {} dim_storage_capacity;
 // clang-format on
 
+// quantities
 QUANTITY_SPEC(traffic_intensity, dim_traffic_intensity);
 QUANTITY_SPEC(traffic_offered_intensity, traffic_intensity);
 QUANTITY_SPEC(traffic_carried_intensity, traffic_intensity);