diff --git a/documentation/sphinx/source/api/iapws.rst b/documentation/sphinx/source/api/iapws.rst
index 06d2db4..b7dc75a 100644
--- a/documentation/sphinx/source/api/iapws.rst
+++ b/documentation/sphinx/source/api/iapws.rst
@@ -14,6 +14,19 @@ Fortran
     
     .. literalinclude:: ../../../../src/iapws_g704.f90
         :language: Fortran
+    
+    IAPWS R283: Critical Constants
+    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+    * `iapws_r283.f90`: Module for IAPWS R2-83
+    
+    .. literalinclude:: ../../../../src/iapws_r283.f90
+        :language: Fortran
+    
+    * `iapws_r283_capi.f90`: C API for IAPWS R2-83.
+    
+    .. literalinclude:: ../../../../src/iapws_r283_capi.f90
+        :language: Fortran
 
     IAPWS G704: Gas solubilities
     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
@@ -23,7 +36,7 @@ Fortran
     .. literalinclude:: ../../../../src/iapws_g704.f90
         :language: Fortran
     
-    * `iapws_g704_capi.f90`: C API for the IAPWS module.
+    * `iapws_g704_capi.f90`: C API for IAPWS G7-04.
     
     .. literalinclude:: ../../../../src/iapws_g704_capi.f90
         :language: Fortran
@@ -36,6 +49,16 @@ C
 .. literalinclude:: ../../../../include/iapws.h
     :language:  C
 
+.. _iapws_r283_capi:
+
+IAPWS R283: Critical Constants
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+* `iapws_r283.h`: C header.
+
+.. literalinclude:: ../../../../include/iapws_r283.h
+    :language: C
+
 IAPWS G704: Gas solubilities
 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
diff --git a/documentation/sphinx/source/api/pyiapws.rst b/documentation/sphinx/source/api/pyiapws.rst
index f9c12be..ae2e269 100644
--- a/documentation/sphinx/source/api/pyiapws.rst
+++ b/documentation/sphinx/source/api/pyiapws.rst
@@ -1,6 +1,15 @@
 pyipaws
 ================
 
+IAPWS R283: Critical Constants
+----------------------------------
+
+.. automodule:: pyiapws.r283
+    :members:
+
+The constants are defined as in the :ref:`C header <iapws_r283_capi>` without
+the prefix *iapws_r283_capi_*.
+
 IAPWS G704: Gas solubilities
 -------------------------------
 
diff --git a/documentation/sphinx/source/getting_started/examples.rst b/documentation/sphinx/source/getting_started/examples.rst
index 49544be..0b86397 100644
--- a/documentation/sphinx/source/getting_started/examples.rst
+++ b/documentation/sphinx/source/getting_started/examples.rst
@@ -3,20 +3,20 @@ Examples
 
 
 Example in Fortran
-^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+------------------------------------------
 
 .. literalinclude:: ../../../../example/example_in_f.f90
     :language: fortran
 
 Example in C
-^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+------------------------------------------
 
 .. literalinclude:: ../../../../example/example_in_c.c
     :language: C
 
 
 Example in Python
-^^^^^^^^^^^^^^^^^^^^^^
+------------------------------------------
 
 .. literalinclude:: ../../../../example/example_in_py.py
     :language: python
diff --git a/example/example_in_c.c b/example/example_in_c.c
index fb47207..711fa6f 100644
--- a/example/example_in_c.c
+++ b/example/example_in_c.c
@@ -13,6 +13,19 @@ int main(void){
     int i;
     int heavywater = 0;
     
+    printf("%s\n", "########################## IAPWS R2-83 ##########################");
+    printf("%s %10.3f %s\n", "Tc in H2O", iapws_r283_capi_Tc_H2O, "K");
+    printf("%s %10.3f %s\n", "pc in H2O", iapws_r283_capi_pc_H2O, "MPa");
+    printf("%s %10.3f %s\n", "rhoc in H2O", iapws_r283_capi_rhoc_H2O, "kg/m3");
+    
+    printf("%s %10.3f %s\n", "Tc in D2O", iapws_r283_capi_Tc_D2O, "K");
+    printf("%s %10.3f %s\n", "pc in D2O", iapws_r283_capi_pc_D2O, "MPa");
+    printf("%s %10.3f %s\n", "rhoc in D2O", iapws_r283_capi_rhoc_D2O, "kg/m3");
+    
+    printf("\n");
+
+
+    printf("%s\n", "########################## IAPWS R2-83 ##########################");
     /* Compute kh and kd in H2O*/
     iapws_g704_capi_kh(&T, gas, heavywater, &kh, strlen(gas), 1);
     printf("Gas=%s\tT=%fC\tkh=%+10.4f\n", gas, T, kh);
diff --git a/example/example_in_f.f90 b/example/example_in_f.f90
index 71c0f06..438de68 100644
--- a/example/example_in_f.f90
+++ b/example/example_in_f.f90
@@ -9,6 +9,17 @@ program example_in_f
     type(iapws_g704_gas_t), pointer :: gases_list(:)
     character(len=:), pointer :: gases_str
 
+    print *, '########################## IAPWS R2-83 ##########################'
+    print "(a, f10.3, a)", "Tc in h2o=", iapws_r283_Tc_H2O, " k"
+    print "(a, f10.3, a)", "pc in h2o=", iapws_r283_pc_H2O, " mpa"
+    print "(a, f10.3, a)", "rhoc in h2o=", iapws_r283_rhoc_H2O, " kg/m3"
+    
+    print "(a, f10.3, a)", "Tc in D2O=", iapws_r283_tc_D2O, " k"
+    print "(a, f10.3, a)", "pc in D2O=", iapws_r283_pc_D2O, " mpa"
+    print "(a, f10.3, a)", "rhoc in D2O=", iapws_r283_rhoc_D2O, " kg/m3"
+    print *, ''
+
+    print *, '########################## IAPWS G7-04 ##########################'
     ! Compute kh and kd in H2O
     T(1) = 25.0d0
     call iapws_g704_kh(T, gas, heavywater, kh)
diff --git a/example/example_in_py.py b/example/example_in_py.py
index 8ff6afe..0bf3da0 100644
--- a/example/example_in_py.py
+++ b/example/example_in_py.py
@@ -2,6 +2,18 @@
 import array
 import pyiapws
 
+print("########################## IAPWS R2-83 ##########################")
+print("Tc in H2O", pyiapws.r283.Tc_H2O, "K")
+print("pc in H2O", pyiapws.r283.pc_H2O, "MPa")
+print("rhoc in H2O", pyiapws.r283.rhoc_H2O, "kg/m3")
+
+print("Tc in D2O", pyiapws.r283.Tc_D2O, "K")
+print("pc in D2O", pyiapws.r283.pc_D2O, "MPa")
+print("rhoc in D2O", pyiapws.r283.rhoc_D2O, "kg/m3")
+
+print("")
+
+print("########################## IAPWS G7-04 ##########################")
 gas  = "O2"
 T = array.array("d", (25.0,))
 
diff --git a/fpm.toml b/fpm.toml
index 5aa76be..47ac18d 100644
--- a/fpm.toml
+++ b/fpm.toml
@@ -39,6 +39,6 @@ main = "test_g704.f90"
 name = "test_g704_capi"
 main = "test_g704_capi.c"
 
-[[test]]
-name = "test_r797"
-main = "test_r797.f90"
\ No newline at end of file
+# [[test]]
+# name = "test_r797"
+# main = "test_r797.f90"
\ No newline at end of file
diff --git a/include/iapws_r283.h b/include/iapws_r283.h
index 8242174..0165a83 100644
--- a/include/iapws_r283.h
+++ b/include/iapws_r283.h
@@ -12,13 +12,13 @@
 #define ADD_IMPORT
 #endif
 
-ADD_IMPORT const double iapws_r283_capi_Tc_H2O; 
-ADD_IMPORT const double iapws_r283_capi_Tc_D2O;
+ADD_IMPORT extern const double iapws_r283_capi_Tc_H2O; 
+ADD_IMPORT extern const double iapws_r283_capi_Tc_D2O;
 
-ADD_IMPORT const double iapws_r283_capi_pc_H2O;
-ADD_IMPORT const double iapws_r283_capi_pc_D2O;
+ADD_IMPORT extern const double iapws_r283_capi_pc_H2O;
+ADD_IMPORT extern const double iapws_r283_capi_pc_D2O;
 
-ADD_IMPORT const double iapws_r283_capi_rhoc_H2O;
-ADD_IMPORT const double iapws_r283_capi_rhoc_D2O;
+ADD_IMPORT extern const double iapws_r283_capi_rhoc_H2O;
+ADD_IMPORT extern const double iapws_r283_capi_rhoc_D2O;
 
 #endif
diff --git a/pywrapper/README.rst b/pywrapper/README.rst
index 58c138b..9d96575 100644
--- a/pywrapper/README.rst
+++ b/pywrapper/README.rst
@@ -8,6 +8,9 @@ Python wrapper around the
 The Fortran library does not need to be installed, the python wrapper embeds all needed dependencies.
 On linux, you might have to install `libgfortran` if it is not distributed with your linux distribution. 
 
+All functions that operate on arrays, more precisely on objects with the buffer protocol, return memory views
+in order to avoid compilation dependencies on 3rd party packages.
+
 .. readme_inclusion_end 
 
 
diff --git a/pywrapper/pyiapws/iapws_r283.c b/pywrapper/pyiapws/iapws_r283.c
index 7f26136..448031f 100644
--- a/pywrapper/pyiapws/iapws_r283.c
+++ b/pywrapper/pyiapws/iapws_r283.c
@@ -45,10 +45,10 @@ PyMODINIT_FUNC PyInit_r283(void)
     Py_INCREF(v);
     
     v = PyFloat_FromDouble(iapws_r283_capi_rhoc_H2O);
-    PyDict_SetItemString(d, "rho_H2O", v);
+    PyDict_SetItemString(d, "rhoc_H2O", v);
     Py_INCREF(v);
     v = PyFloat_FromDouble(iapws_r283_capi_rhoc_D2O);
-    PyDict_SetItemString(d, "rho_D2O", v);
+    PyDict_SetItemString(d, "rhoc_D2O", v);
     Py_INCREF(v);
     
 
diff --git a/pywrapper/pyiapws/tests/test_g704.py b/pywrapper/pyiapws/tests/test_g704.py
index 77ff254..ae18d0a 100644
--- a/pywrapper/pyiapws/tests/test_g704.py
+++ b/pywrapper/pyiapws/tests/test_g704.py
@@ -1,4 +1,4 @@
-r"""Tests"""
+r"""Tests G704."""
 import unittest
 from .. import g704
 import numpy as np
@@ -6,8 +6,8 @@
 T_KELVIN = 273.15
 
 class TestkH(unittest.TestCase):
-    r"""Test pyiawps library."""
-    def test_H2O(self):
+    r"""Test module G704 from pyiawps library."""
+    def test_kh_H2O(self):
         T = np.asarray((300.0-T_KELVIN,))
         m = g704.kh(T, "He", False)
         k = np.asarray(m)
@@ -15,7 +15,7 @@ def test_H2O(self):
         expected = 2.6576
         self.assertAlmostEqual(value, expected, places=4)
     
-    def test_D2O(self):
+    def test_kh_D2O(self):
         T = np.asarray((300.0-T_KELVIN,))
         m = g704.kh(T, "He", True)
         k = np.asarray(m)
@@ -26,7 +26,7 @@ def test_D2O(self):
 
 class TestkD(unittest.TestCase):
     r"""Test pyiawps library."""
-    def test_H2O(self):
+    def test_kd_H2O(self):
         T = np.asarray((300.0-T_KELVIN,))
         m = g704.kd(T, "He", False)
         k = np.asarray(m)
@@ -34,7 +34,7 @@ def test_H2O(self):
         expected = 15.2250
         self.assertAlmostEqual(value, expected, places=4)
     
-    def test_D2O(self):
+    def test_kd_D2O(self):
         T = np.asarray((300.0-T_KELVIN,))
         m = g704.kd(T, "He", True)
         k = np.asarray(m)
diff --git a/pywrapper/pyiapws/tests/test_r283.py b/pywrapper/pyiapws/tests/test_r283.py
new file mode 100644
index 0000000..a79ac1c
--- /dev/null
+++ b/pywrapper/pyiapws/tests/test_r283.py
@@ -0,0 +1,35 @@
+r"""Test R283"""
+import unittest
+from .. import r283
+
+
+class TestH2O(unittest.TestCase):
+    r"""Test module r283 from pyiapws library."""
+    def test_Tc_H2O(self):
+        expected = 647.096
+        value = r283.Tc_H2O
+        self.assertAlmostEqual(value, expected, places=3)
+    def test_pc_H2O(self):
+        expected = 22.064
+        value = r283.pc_H2O
+        self.assertAlmostEqual(value, expected, places=3)
+    def test_rhoc_H2O(self):
+        expected = 322.0
+        value = r283.rhoc_H2O
+        self.assertAlmostEqual(value, expected, places=1)
+
+class TestD2O(unittest.TestCase):
+    r"""Test module r283 from pyiapws library."""
+    def test_Tc_D2O(self):
+        expected = 643.847
+        value = r283.Tc_D2O
+        self.assertAlmostEqual(value, expected, places=3)
+    def test_pc_D2O(self):
+        expected = 21.671
+        value = r283.pc_D2O
+        self.assertAlmostEqual(value, expected, places=3)
+    def test_rhoc_D2O(self):
+        expected = 356.0
+        value = r283.rhoc_D2O
+        self.assertAlmostEqual(value, expected, places=1)
+
diff --git a/pywrapper/setup.py b/pywrapper/setup.py
index c4b46aa..3be8846 100644
--- a/pywrapper/setup.py
+++ b/pywrapper/setup.py
@@ -23,18 +23,18 @@
 
 if __name__ == "__main__":
 
-    mod_ext = Extension(name="pyiapws.g704",
+    mod_g704 = Extension(name="pyiapws.g704",
                         sources=["./pyiapws/iapws_g704.c"],
                         libraries=libraries,
                         library_dirs=library_dirs,
                         runtime_library_dirs=runtime_library_dirs,
                         extra_objects=extra_objects)
-    mod_ext = Extension(name="pyiapws.r283",
+    mod_r283 = Extension(name="pyiapws.r283",
                         sources=["./pyiapws/iapws_r283.c"],
                         libraries=libraries,
                         library_dirs=library_dirs,
                         runtime_library_dirs=runtime_library_dirs,
                         extra_objects=extra_objects)
     
-    setup(ext_modules=[mod_ext])
+    setup(ext_modules=[mod_g704, mod_r283])
     
\ No newline at end of file
diff --git a/test/test_r797.f90 b/test/test_r797.f90.txt
similarity index 100%
rename from test/test_r797.f90
rename to test/test_r797.f90.txt