diff --git a/src/systems/CMakeLists.txt b/src/systems/CMakeLists.txt
index d313f744..40d50f47 100644
--- a/src/systems/CMakeLists.txt
+++ b/src/systems/CMakeLists.txt
@@ -25,8 +25,7 @@ cmake_minimum_required(VERSION 3.19)
 # systems
 add_subdirectory(isq)
 
-# add_subdirectory(isq-iec80000)
-# add_subdirectory(isq-natural)
+add_subdirectory(natural)
 add_subdirectory(si)
 add_subdirectory(si-cgs)
 
diff --git a/src/systems/natural/CMakeLists.txt b/src/systems/natural/CMakeLists.txt
index f48268bc..4ea5fe68 100644
--- a/src/systems/natural/CMakeLists.txt
+++ b/src/systems/natural/CMakeLists.txt
@@ -25,15 +25,5 @@ cmake_minimum_required(VERSION 3.19)
 add_units_module(
     natural
     DEPENDENCIES mp-units::isq
-    HEADERS include/units/isq/natural/acceleration.h
-    include/units/isq/natural/constants.h
-    include/units/isq/natural/energy.h
-    include/units/isq/natural/force.h
-    include/units/isq/natural/length.h
-    include/units/isq/natural/mass.h
-    include/units/isq/natural/momentum.h
-    include/units/isq/natural/natural.h
-    include/units/isq/natural/speed.h
-    include/units/isq/natural/time.h
-    include/units/isq/natural/units.h
+    HEADERS include/units/natural/natural.h
 )
diff --git a/src/systems/natural/include/units/natural/acceleration.h b/src/systems/natural/include/units/natural/acceleration.h
deleted file mode 100644
index 4b6828e1..00000000
--- a/src/systems/natural/include/units/natural/acceleration.h
+++ /dev/null
@@ -1,70 +0,0 @@
-// The MIT License (MIT)
-//
-// Copyright (c) 2018 Mateusz Pusz
-//
-// Permission is hereby granted, free of charge, to any person obtaining a copy
-// of this software and associated documentation files (the "Software"), to deal
-// in the Software without restriction, including without limitation the rights
-// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
-// copies of the Software, and to permit persons to whom the Software is
-// furnished to do so, subject to the following conditions:
-//
-// The above copyright notice and this permission notice shall be included in all
-// copies or substantial portions of the Software.
-//
-// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
-// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
-// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
-// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
-// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
-// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
-// SOFTWARE.
-
-#pragma once
-
-#include <units/isq/natural/length.h>
-#include <units/isq/natural/time.h>
-
-// IWYU pragma: begin_exports
-#include <units/isq/dimensions/acceleration.h>
-#include <units/isq/natural/units.h>
-#include <units/quantity.h>
-#include <units/reference.h>
-#include <units/symbol_text.h>
-// IWYU pragma: end_exports
-
-namespace units::isq::natural {
-
-struct dim_acceleration : isq::dim_acceleration<dim_acceleration, gigaelectronvolt, dim_length, dim_time> {};
-
-template<UnitOf<dim_acceleration> U, Representation Rep = double>
-using acceleration = quantity<dim_acceleration, U, Rep>;
-
-#ifndef UNITS_NO_REFERENCES
-
-namespace acceleration_references {
-
-inline constexpr auto GeV = reference<dim_acceleration, gigaelectronvolt>{};
-
-}  // namespace acceleration_references
-
-namespace references {
-
-using namespace acceleration_references;
-
-}  // namespace references
-
-#endif  // UNITS_NO_REFERENCES
-
-}  // namespace units::isq::natural
-
-#ifndef UNITS_NO_ALIASES
-
-namespace units::aliases::isq::natural::inline acceleration {
-
-template<Representation Rep = double>
-using GeV = units::isq::natural::acceleration<units::isq::natural::gigaelectronvolt, Rep>;
-
-}  // namespace units::aliases::isq::natural::inline acceleration
-
-#endif  // UNITS_NO_ALIASES
diff --git a/src/systems/natural/include/units/natural/constants.h b/src/systems/natural/include/units/natural/constants.h
deleted file mode 100644
index c570a589..00000000
--- a/src/systems/natural/include/units/natural/constants.h
+++ /dev/null
@@ -1,32 +0,0 @@
-// The MIT License (MIT)
-//
-// Copyright (c) 2018 Mateusz Pusz
-//
-// Permission is hereby granted, free of charge, to any person obtaining a copy
-// of this software and associated documentation files (the "Software"), to deal
-// in the Software without restriction, including without limitation the rights
-// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
-// copies of the Software, and to permit persons to whom the Software is
-// furnished to do so, subject to the following conditions:
-//
-// The above copyright notice and this permission notice shall be included in all
-// copies or substantial portions of the Software.
-//
-// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
-// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
-// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
-// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
-// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
-// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
-// SOFTWARE.
-
-#pragma once
-
-#include <units/isq/natural/speed.h>
-
-namespace units::isq::natural {
-
-template<Representation Rep = double>
-inline constexpr auto speed_of_light = speed<one, Rep>(1);
-
-}  // namespace units::isq::natural
diff --git a/src/systems/natural/include/units/natural/energy.h b/src/systems/natural/include/units/natural/energy.h
deleted file mode 100644
index 84587a0a..00000000
--- a/src/systems/natural/include/units/natural/energy.h
+++ /dev/null
@@ -1,70 +0,0 @@
-// The MIT License (MIT)
-//
-// Copyright (c) 2018 Mateusz Pusz
-//
-// Permission is hereby granted, free of charge, to any person obtaining a copy
-// of this software and associated documentation files (the "Software"), to deal
-// in the Software without restriction, including without limitation the rights
-// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
-// copies of the Software, and to permit persons to whom the Software is
-// furnished to do so, subject to the following conditions:
-//
-// The above copyright notice and this permission notice shall be included in all
-// copies or substantial portions of the Software.
-//
-// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
-// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
-// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
-// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
-// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
-// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
-// SOFTWARE.
-
-#pragma once
-
-#include <units/isq/natural/force.h>
-#include <units/isq/natural/length.h>
-
-// IWYU pragma: begin_exports
-#include <units/isq/dimensions/energy.h>
-#include <units/isq/natural/units.h>
-#include <units/quantity.h>
-#include <units/reference.h>
-#include <units/symbol_text.h>
-// IWYU pragma: end_exports
-
-namespace units::isq::natural {
-
-struct dim_energy : isq::dim_energy<dim_energy, gigaelectronvolt, dim_force, dim_length> {};
-
-template<UnitOf<dim_energy> U, Representation Rep = double>
-using energy = quantity<dim_energy, U, Rep>;
-
-#ifndef UNITS_NO_REFERENCES
-
-namespace energy_references {
-
-inline constexpr auto GeV = reference<dim_energy, gigaelectronvolt>{};
-
-}  // namespace energy_references
-
-namespace references {
-
-using namespace energy_references;
-
-}  // namespace references
-
-#endif  // UNITS_NO_REFERENCES
-
-}  // namespace units::isq::natural
-
-#ifndef UNITS_NO_ALIASES
-
-namespace units::aliases::isq::natural::inline energy {
-
-template<Representation Rep = double>
-using GeV = units::isq::natural::energy<units::isq::natural::gigaelectronvolt, Rep>;
-
-}  // namespace units::aliases::isq::natural::inline energy
-
-#endif  // UNITS_NO_ALIASES
diff --git a/src/systems/natural/include/units/natural/force.h b/src/systems/natural/include/units/natural/force.h
deleted file mode 100644
index 26921dfc..00000000
--- a/src/systems/natural/include/units/natural/force.h
+++ /dev/null
@@ -1,70 +0,0 @@
-// The MIT License (MIT)
-//
-// Copyright (c) 2018 Mateusz Pusz
-//
-// Permission is hereby granted, free of charge, to any person obtaining a copy
-// of this software and associated documentation files (the "Software"), to deal
-// in the Software without restriction, including without limitation the rights
-// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
-// copies of the Software, and to permit persons to whom the Software is
-// furnished to do so, subject to the following conditions:
-//
-// The above copyright notice and this permission notice shall be included in all
-// copies or substantial portions of the Software.
-//
-// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
-// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
-// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
-// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
-// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
-// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
-// SOFTWARE.
-
-#pragma once
-
-#include <units/isq/natural/acceleration.h>
-#include <units/isq/natural/mass.h>
-
-// IWYU pragma: begin_exports
-#include <units/isq/dimensions/force.h>
-#include <units/isq/natural/units.h>
-#include <units/quantity.h>
-#include <units/reference.h>
-#include <units/symbol_text.h>
-// IWYU pragma: end_exports
-
-namespace units::isq::natural {
-
-struct dim_force : isq::dim_force<dim_force, square_gigaelectronvolt, dim_mass, dim_acceleration> {};
-
-template<UnitOf<dim_force> U, Representation Rep = double>
-using force = quantity<dim_force, U, Rep>;
-
-#ifndef UNITS_NO_REFERENCES
-
-namespace force_references {
-
-inline constexpr auto GeV2 = reference<dim_force, square_gigaelectronvolt>{};
-
-}  // namespace force_references
-
-namespace references {
-
-using namespace force_references;
-
-}  // namespace references
-
-#endif  // UNITS_NO_REFERENCES
-
-}  // namespace units::isq::natural
-
-#ifndef UNITS_NO_ALIASES
-
-namespace units::aliases::isq::natural::inline force {
-
-template<Representation Rep = double>
-using GeV2 = units::isq::natural::force<units::isq::natural::square_gigaelectronvolt, Rep>;
-
-}  // namespace units::aliases::isq::natural::inline force
-
-#endif  // UNITS_NO_ALIASES
diff --git a/src/systems/natural/include/units/natural/length.h b/src/systems/natural/include/units/natural/length.h
deleted file mode 100644
index 7174a525..00000000
--- a/src/systems/natural/include/units/natural/length.h
+++ /dev/null
@@ -1,67 +0,0 @@
-// The MIT License (MIT)
-//
-// Copyright (c) 2018 Mateusz Pusz
-//
-// Permission is hereby granted, free of charge, to any person obtaining a copy
-// of this software and associated documentation files (the "Software"), to deal
-// in the Software without restriction, including without limitation the rights
-// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
-// copies of the Software, and to permit persons to whom the Software is
-// furnished to do so, subject to the following conditions:
-//
-// The above copyright notice and this permission notice shall be included in all
-// copies or substantial portions of the Software.
-//
-// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
-// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
-// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
-// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
-// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
-// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
-// SOFTWARE.
-
-#pragma once
-
-// IWYU pragma: begin_exports
-#include <units/isq/dimensions/length.h>
-#include <units/isq/natural/units.h>
-#include <units/quantity.h>
-#include <units/reference.h>
-#include <units/symbol_text.h>
-// IWYU pragma: end_exports
-
-namespace units::isq::natural {
-
-struct dim_length : isq::dim_length<inverted_gigaelectronvolt> {};
-
-template<UnitOf<dim_length> U, Representation Rep = double>
-using length = quantity<dim_length, U, Rep>;
-
-#ifndef UNITS_NO_REFERENCES
-
-namespace length_references {
-
-inline constexpr auto inv_GeV = reference<dim_length, inverted_gigaelectronvolt>{};
-
-}  // namespace length_references
-
-namespace references {
-
-using namespace length_references;
-
-}  // namespace references
-
-#endif  // UNITS_NO_REFERENCES
-
-}  // namespace units::isq::natural
-
-#ifndef UNITS_NO_ALIASES
-
-namespace units::aliases::isq::natural::inline length {
-
-template<Representation Rep = double>
-using inv_GeV = units::isq::natural::length<units::isq::natural::inverted_gigaelectronvolt, Rep>;
-
-}  // namespace units::aliases::isq::natural::inline length
-
-#endif  // UNITS_NO_ALIASES
diff --git a/src/systems/natural/include/units/natural/mass.h b/src/systems/natural/include/units/natural/mass.h
deleted file mode 100644
index d9ff98de..00000000
--- a/src/systems/natural/include/units/natural/mass.h
+++ /dev/null
@@ -1,67 +0,0 @@
-// The MIT License (MIT)
-//
-// Copyright (c) 2018 Mateusz Pusz
-//
-// Permission is hereby granted, free of charge, to any person obtaining a copy
-// of this software and associated documentation files (the "Software"), to deal
-// in the Software without restriction, including without limitation the rights
-// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
-// copies of the Software, and to permit persons to whom the Software is
-// furnished to do so, subject to the following conditions:
-//
-// The above copyright notice and this permission notice shall be included in all
-// copies or substantial portions of the Software.
-//
-// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
-// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
-// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
-// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
-// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
-// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
-// SOFTWARE.
-
-#pragma once
-
-// IWYU pragma: begin_exports
-#include <units/isq/dimensions/mass.h>
-#include <units/isq/natural/units.h>
-#include <units/quantity.h>
-#include <units/reference.h>
-#include <units/symbol_text.h>
-// IWYU pragma: end_exports
-
-namespace units::isq::natural {
-
-struct dim_mass : isq::dim_mass<gigaelectronvolt> {};
-
-template<UnitOf<dim_mass> U, Representation Rep = double>
-using mass = quantity<dim_mass, U, Rep>;
-
-#ifndef UNITS_NO_REFERENCES
-
-namespace mass_references {
-
-inline constexpr auto GeV = reference<dim_mass, gigaelectronvolt>{};
-
-}  // namespace mass_references
-
-namespace references {
-
-using namespace mass_references;
-
-}  // namespace references
-
-#endif  // UNITS_NO_REFERENCES
-
-}  // namespace units::isq::natural
-
-#ifndef UNITS_NO_ALIASES
-
-namespace units::aliases::isq::natural::inline mass {
-
-template<Representation Rep = double>
-using GeV = units::isq::natural::mass<units::isq::natural::gigaelectronvolt, Rep>;
-
-}  // namespace units::aliases::isq::natural::inline mass
-
-#endif  // UNITS_NO_ALIASES
diff --git a/src/systems/natural/include/units/natural/momentum.h b/src/systems/natural/include/units/natural/momentum.h
deleted file mode 100644
index 32f633d5..00000000
--- a/src/systems/natural/include/units/natural/momentum.h
+++ /dev/null
@@ -1,70 +0,0 @@
-// The MIT License (MIT)
-//
-// Copyright (c) 2018 Mateusz Pusz
-//
-// Permission is hereby granted, free of charge, to any person obtaining a copy
-// of this software and associated documentation files (the "Software"), to deal
-// in the Software without restriction, including without limitation the rights
-// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
-// copies of the Software, and to permit persons to whom the Software is
-// furnished to do so, subject to the following conditions:
-//
-// The above copyright notice and this permission notice shall be included in all
-// copies or substantial portions of the Software.
-//
-// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
-// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
-// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
-// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
-// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
-// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
-// SOFTWARE.
-
-#pragma once
-
-#include <units/isq/natural/mass.h>
-#include <units/isq/natural/speed.h>
-
-// IWYU pragma: begin_exports
-#include <units/isq/dimensions/momentum.h>
-#include <units/isq/natural/units.h>
-#include <units/quantity.h>
-#include <units/reference.h>
-#include <units/symbol_text.h>
-// IWYU pragma: end_exports
-
-namespace units::isq::natural {
-
-struct dim_momentum : isq::dim_momentum<dim_momentum, gigaelectronvolt, dim_mass, dim_speed> {};
-
-template<UnitOf<dim_momentum> U, Representation Rep = double>
-using momentum = quantity<dim_momentum, U, Rep>;
-
-#ifndef UNITS_NO_REFERENCES
-
-namespace momentum_references {
-
-inline constexpr auto GeV = reference<dim_momentum, gigaelectronvolt>{};
-
-}  // namespace momentum_references
-
-namespace references {
-
-using namespace momentum_references;
-
-}  // namespace references
-
-#endif  // UNITS_NO_REFERENCES
-
-}  // namespace units::isq::natural
-
-#ifndef UNITS_NO_ALIASES
-
-namespace units::aliases::isq::natural::inline momentum {
-
-template<Representation Rep = double>
-using GeV = units::isq::natural::momentum<units::isq::natural::gigaelectronvolt, Rep>;
-
-}  // namespace units::aliases::isq::natural::inline momentum
-
-#endif  // UNITS_NO_ALIASES
diff --git a/src/systems/natural/include/units/natural/natural.h b/src/systems/natural/include/units/natural/natural.h
index 09dbcfbd..a9d22eb3 100644
--- a/src/systems/natural/include/units/natural/natural.h
+++ b/src/systems/natural/include/units/natural/natural.h
@@ -22,14 +22,39 @@
 
 #pragma once
 
-// IWYU pragma: begin_exports
-#include <units/isq/natural/acceleration.h>
-#include <units/isq/natural/constants.h>
-#include <units/isq/natural/energy.h>
-#include <units/isq/natural/force.h>
-#include <units/isq/natural/length.h>
-#include <units/isq/natural/mass.h>
-#include <units/isq/natural/momentum.h>
-#include <units/isq/natural/speed.h>
-#include <units/isq/natural/time.h>
-// IWYU pragma: end_exports
+#include <units/isq/mechanics.h>
+#include <units/isq/space_and_time.h>
+#include <units/si/prefixes.h>
+#include <units/system_reference.h>
+#include <units/unit.h>
+
+namespace units::natural {
+
+// clang-format off
+// units
+inline constexpr struct electronvolt : named_unit<"eV"> {} electronvolt;
+inline constexpr struct gigaelectronvolt : decltype(si::giga<electronvolt>) {} gigaelectronvolt;
+
+// system references
+inline constexpr struct time : system_reference<isq::time, 1 / gigaelectronvolt> {} time;
+inline constexpr struct length : system_reference<isq::length, 1 / gigaelectronvolt> {} length;
+inline constexpr struct mass : system_reference<isq::mass, gigaelectronvolt> {} mass;
+inline constexpr struct velocity : system_reference<isq::velocity, one> {} velocity;
+inline constexpr struct speed : system_reference<isq::speed, one> {} speed;
+inline constexpr struct acceleration : system_reference<isq::acceleration, gigaelectronvolt> {} acceleration;
+inline constexpr struct momentum : system_reference<isq::momentum, gigaelectronvolt> {} momentum;
+inline constexpr struct force : system_reference<isq::force, square<gigaelectronvolt>> {} force;
+inline constexpr struct energy : system_reference<isq::mechanical_energy, gigaelectronvolt> {} energy;
+// clang-format on
+
+// constants
+inline constexpr auto speed_of_light_in_vacuum = speed[one];
+
+namespace unit_symbols {
+
+inline constexpr auto GeV = gigaelectronvolt;
+inline constexpr auto GeV2 = square<gigaelectronvolt>;
+
+}  // namespace unit_symbols
+
+}  // namespace units::natural
diff --git a/src/systems/natural/include/units/natural/speed.h b/src/systems/natural/include/units/natural/speed.h
deleted file mode 100644
index 29f388cc..00000000
--- a/src/systems/natural/include/units/natural/speed.h
+++ /dev/null
@@ -1,44 +0,0 @@
-// The MIT License (MIT)
-//
-// Copyright (c) 2018 Mateusz Pusz
-//
-// Permission is hereby granted, free of charge, to any person obtaining a copy
-// of this software and associated documentation files (the "Software"), to deal
-// in the Software without restriction, including without limitation the rights
-// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
-// copies of the Software, and to permit persons to whom the Software is
-// furnished to do so, subject to the following conditions:
-//
-// The above copyright notice and this permission notice shall be included in all
-// copies or substantial portions of the Software.
-//
-// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
-// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
-// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
-// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
-// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
-// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
-// SOFTWARE.
-
-#pragma once
-
-#include <units/isq/natural/length.h>
-#include <units/isq/natural/time.h>
-
-// IWYU pragma: begin_exports
-#include <units/generic/dimensionless.h>
-#include <units/isq/dimensions/speed.h>
-#include <units/isq/natural/units.h>
-#include <units/quantity.h>
-#include <units/reference.h>
-#include <units/symbol_text.h>
-// IWYU pragma: end_exports
-
-namespace units::isq::natural {
-
-struct dim_speed : isq::dim_speed<dim_speed, one, dim_length, dim_time> {};
-
-template<UnitOf<dim_speed> U, Representation Rep = double>
-using speed = quantity<dim_speed, U, Rep>;
-
-}  // namespace units::isq::natural
diff --git a/src/systems/natural/include/units/natural/time.h b/src/systems/natural/include/units/natural/time.h
deleted file mode 100644
index fc82e5ea..00000000
--- a/src/systems/natural/include/units/natural/time.h
+++ /dev/null
@@ -1,67 +0,0 @@
-// The MIT License (MIT)
-//
-// Copyright (c) 2018 Mateusz Pusz
-//
-// Permission is hereby granted, free of charge, to any person obtaining a copy
-// of this software and associated documentation files (the "Software"), to deal
-// in the Software without restriction, including without limitation the rights
-// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
-// copies of the Software, and to permit persons to whom the Software is
-// furnished to do so, subject to the following conditions:
-//
-// The above copyright notice and this permission notice shall be included in all
-// copies or substantial portions of the Software.
-//
-// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
-// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
-// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
-// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
-// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
-// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
-// SOFTWARE.
-
-#pragma once
-
-// IWYU pragma: begin_exports
-#include <units/isq/dimensions/time.h>
-#include <units/isq/natural/units.h>
-#include <units/quantity.h>
-#include <units/reference.h>
-#include <units/symbol_text.h>
-// IWYU pragma: end_exports
-
-namespace units::isq::natural {
-
-struct dim_time : isq::dim_time<inverted_gigaelectronvolt> {};
-
-template<UnitOf<dim_time> U, Representation Rep = double>
-using time = quantity<dim_time, U, Rep>;
-
-#ifndef UNITS_NO_REFERENCES
-
-namespace time_references {
-
-inline constexpr auto inv_GeV = reference<dim_time, inverted_gigaelectronvolt>{};
-
-}  // namespace time_references
-
-namespace references {
-
-using namespace time_references;
-
-}  // namespace references
-
-#endif  // UNITS_NO_REFERENCES
-
-}  // namespace units::isq::natural
-
-#ifndef UNITS_NO_ALIASES
-
-namespace units::aliases::isq::natural::inline time {
-
-template<Representation Rep = double>
-using inv_GeV = units::isq::natural::time<units::isq::natural::inverted_gigaelectronvolt, Rep>;
-
-}  // namespace units::aliases::isq::natural::inline time
-
-#endif  // UNITS_NO_ALIASES
diff --git a/src/systems/natural/include/units/natural/units.h b/src/systems/natural/include/units/natural/units.h
deleted file mode 100644
index 82712296..00000000
--- a/src/systems/natural/include/units/natural/units.h
+++ /dev/null
@@ -1,44 +0,0 @@
-// The MIT License (MIT)
-//
-// Copyright (c) 2018 Mateusz Pusz
-//
-// Permission is hereby granted, free of charge, to any person obtaining a copy
-// of this software and associated documentation files (the "Software"), to deal
-// in the Software without restriction, including without limitation the rights
-// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
-// copies of the Software, and to permit persons to whom the Software is
-// furnished to do so, subject to the following conditions:
-//
-// The above copyright notice and this permission notice shall be included in all
-// copies or substantial portions of the Software.
-//
-// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
-// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
-// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
-// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
-// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
-// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
-// SOFTWARE.
-
-#pragma once
-
-// IWYU pragma: begin_exports
-#include <units/symbol_text.h>
-// IWYU pragma: end_exports
-
-#include <units/isq/si/prefixes.h>
-#include <units/unit.h>
-
-namespace units::isq::natural {
-
-struct electronvolt : named_unit<electronvolt, "eV"> {};
-struct gigaelectronvolt : prefixed_unit<gigaelectronvolt, si::giga, electronvolt> {};
-struct inverted_gigaelectronvolt : named_unit<inverted_gigaelectronvolt, basic_symbol_text{"GeV⁻¹", "GeV^-1"}> {};
-struct square_gigaelectronvolt : named_unit<square_gigaelectronvolt, basic_symbol_text{"GeV²", "GeV^2"}> {};
-
-// NOTE: eV as a base unit with no relation to joule prevents us from going back
-// from natural units to SI. Do we need such a support or should we treat
-// natural units as an isolated island with ev = 1 which simplifies all
-// the maths a lot?
-
-}  // namespace units::isq::natural