diff --git a/gradation.py b/gradation.py
new file mode 100644
index 0000000..6b90c1e
--- /dev/null
+++ b/gradation.py
@@ -0,0 +1,60 @@
+
+from __future__ import annotations
+from typing import Union
+import math
+
+
+class Gradation:
+    grams_per_liter: int
+
+    def __init__(self, grams_per_liter: Union[float, int]):
+        self.grams_per_liter = int(grams_per_liter)
+
+    def get_nm(self) -> float:
+        return self.grams_per_liter / 10
+
+    def get_kmw(self) -> float:
+        return 0.732 * self.get_nm() + 3.2
+
+    def get_oe(self) -> float:
+        return self.get_kmw() * (4.54 + 0.022 * self.get_kmw())
+
+    def get_be(self) -> float:
+        return self.get_kmw() / 1.53
+
+    def get_bx(self) -> float:
+        return self.get_be() / 0.55
+
+    @staticmethod
+    def from_nm(nm: float) -> Gradation:
+        return Gradation(nm * 10)
+
+    @staticmethod
+    def from_kmw(kmw: float) -> Gradation:
+        return Gradation.from_nm((kmw - 3.2) / 0.732)
+
+    @staticmethod
+    def from_oe(oe: float) -> Gradation:
+        return Gradation.from_kmw((-4.54 + math.sqrt(4.54 * 4.54 - 4 * 0.022 * -oe)) / (2 * 0.022))
+
+
+def test():
+    g1 = Gradation.from_kmw(15)
+    assert round(g1.get_kmw(), 1) == 15
+    assert round(g1.get_oe(), 0) == 73
+
+
+def print_all():
+    for i in range(14 * 2, 22 * 2):
+        kmw = i / 2
+        g = Gradation.from_kmw(kmw)
+        print(f"{kmw} -> {g.get_kmw():.1f} °KMW, {g.get_oe():3.0f} °Oe, {g.get_nm():.1f} °NM, {g.grams_per_liter}")
+    print("================================")
+    for oe in range(65, 110):
+        g = Gradation.from_oe(oe)
+        print(f"{oe:3} -> {g.get_kmw():.1f} °KMW, {g.get_oe():3.0f} °Oe, {g.get_nm():.1f} °NM, {g.grams_per_liter}")
+
+
+if __name__ == '__main__':
+    print_all()
+    test()