diff --git a/.gitignore b/.gitignore
index 7acc6cc..cbefbbf 100644
--- a/.gitignore
+++ b/.gitignore
@@ -1,5 +1,5 @@
-Elwig/obj/
-Elwig/bin/
+obj/
+bin/
 *.user
 .vs
 .idea
diff --git a/Elwig.sln b/Elwig.sln
index 9cdfaf0..d308563 100644
--- a/Elwig.sln
+++ b/Elwig.sln
@@ -1,10 +1,11 @@
-
 Microsoft Visual Studio Solution File, Format Version 12.00
 # Visual Studio Version 17
 VisualStudioVersion = 17.3.32929.385
 MinimumVisualStudioVersion = 10.0.40219.1
 Project("{9A19103F-16F7-4668-BE54-9A1E7A4F7556}") = "Elwig", "Elwig\Elwig.csproj", "{00868460-16F6-4B48-AA9B-998F6263693B}"
 EndProject
+Project("{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}") = "Tests", "Tests\Tests.csproj", "{AF4B84F8-08E6-409C-9E94-D7D990469597}"
+EndProject
 Global
 	GlobalSection(SolutionConfigurationPlatforms) = preSolution
 		Debug|Any CPU = Debug|Any CPU
@@ -15,6 +16,10 @@ Global
 		{00868460-16F6-4B48-AA9B-998F6263693B}.Debug|Any CPU.Build.0 = Debug|Any CPU
 		{00868460-16F6-4B48-AA9B-998F6263693B}.Release|Any CPU.ActiveCfg = Release|Any CPU
 		{00868460-16F6-4B48-AA9B-998F6263693B}.Release|Any CPU.Build.0 = Release|Any CPU
+		{AF4B84F8-08E6-409C-9E94-D7D990469597}.Debug|Any CPU.ActiveCfg = Debug|Any CPU
+		{AF4B84F8-08E6-409C-9E94-D7D990469597}.Debug|Any CPU.Build.0 = Debug|Any CPU
+		{AF4B84F8-08E6-409C-9E94-D7D990469597}.Release|Any CPU.ActiveCfg = Release|Any CPU
+		{AF4B84F8-08E6-409C-9E94-D7D990469597}.Release|Any CPU.Build.0 = Release|Any CPU
 	EndGlobalSection
 	GlobalSection(SolutionProperties) = preSolution
 		HideSolutionNode = FALSE
diff --git a/Elwig/Helpers/Utils.cs b/Elwig/Helpers/Utils.cs
index e4a350d..6ff4b59 100644
--- a/Elwig/Helpers/Utils.cs
+++ b/Elwig/Helpers/Utils.cs
@@ -108,17 +108,17 @@ namespace Elwig.Helpers {
         }
 
         public static double OeToKmw(double oe) {
-            return Math.Round((-4.54 + Math.Sqrt(4.54 * 4.54 - 4 * 0.022 * -oe)) / 2 * 0.022, 1);
+            return Math.Round((-4.54 + Math.Sqrt(4.54 * 4.54 - 4 * 0.022 * -oe)) / (2 * 0.022), 1);
         }
 
         public static decimal DecFromDb(long value, byte precision) {
             bool neg = value < 0;
-            if (neg)  value = -value;
-            return new decimal((int)(value & 0xFFFFFFFF), (int)((value >> 32) & 0x7FFFFFFF), 0, neg, precision);
+            if (neg) value = -value;
+            return new((int)(value & 0xFFFFFFFF), (int)((value >> 32) & 0x7FFFFFFF), 0, neg, precision);
         }
 
         public static long DecToDb(decimal value, byte precision) {
-            return (long)decimal.Round(value * precision, 0);
+            return (long)decimal.Round(value * (decimal)Math.Pow(10, precision), 0);
         }
     }
 }
diff --git a/Tests/HelpersUtilsTest.cs b/Tests/HelpersUtilsTest.cs
new file mode 100644
index 0000000..a775177
--- /dev/null
+++ b/Tests/HelpersUtilsTest.cs
@@ -0,0 +1,46 @@
+using Elwig.Helpers;
+
+namespace Tests {
+    [TestClass]
+    public class HelpersUtilsTest {
+
+        private static readonly double[,] Gradation = new double[,] {
+            { 14.0,  68.0 },
+            { 15.0,  73.0 },
+            { 17.1,  84.0 },
+            { 19.0,  94.0 },
+            { 21.0, 105.0 },
+            { 25.0, 127.0 },
+            { 27.1, 139.0 },
+            { 30.0, 156.0 },
+        };
+
+        [TestMethod]
+        public void Test_KmwToOe() {
+            for (int i = 0; i < Gradation.GetLength(0); i++) {
+                Assert.AreEqual(Gradation[i, 1], Utils.KmwToOe(Gradation[i, 0]));
+            }
+        }
+
+        [TestMethod]
+        public void Test_OeToKmw() {
+            for (int i = 0; i < Gradation.GetLength(0); i++) {
+                Assert.AreEqual(Gradation[i, 0], Utils.OeToKmw(Gradation[i, 1]));
+            }
+        }
+
+        [TestMethod]
+        public void Test_DecFromDb() {
+            Assert.AreEqual(10.67M, Utils.DecFromDb(10670, 3));
+            Assert.AreEqual(-100.9999M, Utils.DecFromDb(-1009999, 4));
+            Assert.AreEqual(0.01M, Utils.DecFromDb(1, 2));
+        }
+
+        [TestMethod]
+        public void Test_DecToDb() {
+            Assert.AreEqual(21948, Utils.DecToDb(219.48M, 2));
+            Assert.AreEqual(-12345, Utils.DecToDb(-1.2345M, 4));
+            Assert.AreEqual(99190, Utils.DecToDb(99190, 0));
+        }
+    }
+}
\ No newline at end of file
diff --git a/Tests/Tests.csproj b/Tests/Tests.csproj
new file mode 100644
index 0000000..d92d858
--- /dev/null
+++ b/Tests/Tests.csproj
@@ -0,0 +1,23 @@
+<Project Sdk="Microsoft.NET.Sdk">
+
+  <PropertyGroup>
+    <TargetFramework>net7.0-windows</TargetFramework>
+    <ImplicitUsings>enable</ImplicitUsings>
+    <Nullable>enable</Nullable>
+
+    <IsPackable>false</IsPackable>
+    <IsTestProject>true</IsTestProject>
+  </PropertyGroup>
+
+  <ItemGroup>
+    <PackageReference Include="Microsoft.NET.Test.Sdk" Version="17.3.2" />
+    <PackageReference Include="MSTest.TestAdapter" Version="2.2.10" />
+    <PackageReference Include="MSTest.TestFramework" Version="2.2.10" />
+    <PackageReference Include="coverlet.collector" Version="3.1.2" />
+  </ItemGroup>
+
+  <ItemGroup>
+    <ProjectReference Include="..\Elwig\Elwig.csproj" />
+  </ItemGroup>
+
+</Project>
diff --git a/Tests/Usings.cs b/Tests/Usings.cs
new file mode 100644
index 0000000..ab67c7e
--- /dev/null
+++ b/Tests/Usings.cs
@@ -0,0 +1 @@
+global using Microsoft.VisualStudio.TestTools.UnitTesting;
\ No newline at end of file