Added implicit conversion from Scalar to double

CodeGen/Generators/UnitsNetGen/UnitTestBaseClassGenerator.cs

@@ -545,13 +545,20 @@ public void ToString_NullProvider_EqualsCurrentUICulture()
             Assert.Equal(quantity.ToString(CultureInfo.CurrentUICulture, ""g""), quantity.ToString(null, ""g""));
         }}
 
+");
+            if (!_quantity.Name.Equals("Scalar"))
+            {
+                Writer.WL($@"
 
         [Fact]
         public void Convert_ToBool_ThrowsInvalidCastException()
         {{
             var quantity = {_quantity.Name}.From{_baseUnit.PluralName}(1.0);
             Assert.Throws<InvalidCastException>(() => Convert.ToBoolean(quantity));
         }}
+");
+            }
+            Writer.WL($@"
 
         [Fact]
         public void Convert_ToByte_EqualsValueAsSameType()

UnitsNet.Tests/CustomCode/ScalarTests.cs

@@ -27,6 +27,18 @@ public class ScalarTests : ScalarTestsBase
         // Override properties in base class here
         protected override double AmountInOneAmount => 1;
         protected override bool SupportsSIUnitSystem => false;
-
+
+        [Theory]
+        [InlineData(0)]
+        [InlineData(1.0)]
+        [InlineData(-Math.PI)]
+        public void ImplicitCast_ToDouble_IsAmount(double amount)
+        {
+            var scalar = Scalar.FromAmount(amount);
+            double asDouble = scalar;
+
+            Assert.Equal(asDouble, scalar.Amount);
+        }
     }
+
 }

UnitsNet/CustomCode/Quantities/Scalar.extra.cs

@@ -0,0 +1,14 @@
+// Licensed under MIT No Attribution, see LICENSE file at the root.
+// Copyright 2013 Andreas Gullberg Larsen ([email protected]). Maintained at https://github.com/angularsen/UnitsNet.
+
+namespace UnitsNet
+{
+    public partial struct Scalar
+    {
+        /// <summary>Defines an implicit conversion of a <see cref="Scalar"/> to a <see cref="double"/>.</summary>
+        public static implicit operator double(Scalar scalar)
+        {
+            return scalar.Amount;
+        }
+    }
+}