diff --git a/DeathSocket/Domain.fs b/DeathSocket/Domain.fs
index 4bde64e..18bc1a6 100644
--- a/DeathSocket/Domain.fs
+++ b/DeathSocket/Domain.fs
@@ -97,7 +97,7 @@
               ///The number of columns the grid will have.
               columns: int }
 
-        /// Discriminated Union representing the various specification types
+        /// A Discriminated Union representing the various specification types
         /// Death Socket can use to apply a grid to an image.
         type ImageSpec =
             | Brush of BrushSpec
@@ -105,9 +105,14 @@
             | Skia of SkiaSpec
             | SkiaRGB of SkiaRGBSpec
 
-        /// Discriminated Union representing the graphics libraries used by
-        /// Death Socket. Useful for selecting which one you want to use.
-        /// System.Drawing for using Windows/Mono and SkiaSharp for Xamarin.
+        /// A Discriminated Union representing a type of image. The type refers
+        /// to the graphics library used to read the image file.
+        /// The graphics library determines how the image is stored in memory
+        /// and the functions you can perform on it.
+        /// When creating an ImageType, pass in the file path of the image
+        /// as a string. If you are on Windows or using Mono, SystemDrawing is
+        /// the recommended choice. If you using Xamarin, SkiaSharp is the
+        /// recommended choice.
         type ImageType =
             | SkiaSharp of string
             | SystemDrawing of string
\ No newline at end of file
diff --git a/DeathSocket/GridPainter.fs b/DeathSocket/GridPainter.fs
index 726e2ae..4b986b1 100644
--- a/DeathSocket/GridPainter.fs
+++ b/DeathSocket/GridPainter.fs
@@ -51,8 +51,6 @@ namespace DeathSocket
                     printfn "File could not be found at %s" ex.Message
             }
 
-        // NOT TESTED
-
         /// <summary>
         /// Determines the current scale an image is viewed at (E.G. scaled
         /// preview in image viewer). The (pen) line thickness is then updated
@@ -75,7 +73,7 @@ namespace DeathSocket
         /// you should not need to use this function when using them.
         /// </remarks>
         let scaleLineThickness (previewDimension: double) (actualDimension: double) (lineThickness: double) =
-            lineThickness / (previewDimension / actualDimension)
+            setLineThickness previewDimension actualDimension lineThickness
 
         // NOT TESTED
 
diff --git a/DeathSocket/ImageServices.fs b/DeathSocket/ImageServices.fs
index 12cba6b..c6408c3 100644
--- a/DeathSocket/ImageServices.fs
+++ b/DeathSocket/ImageServices.fs
@@ -6,6 +6,12 @@
     open DeathSocket
     open ColourServices
     open SkiaSharp
+    open System
+
+    let setLineThickness pDimension aDimension lineWidth =
+        if (pDimension <= 0.0 || aDimension <= 0.0 || lineWidth <= 0.0) then
+            raise (new DivideByZeroException ("[ERROR] The images height and width must be greater than 0."))
+        else lineWidth / (pDimension / aDimension)
 
     // SkiaSharp Functions
     // ========================================================================
diff --git a/TestCentre/LibraryTests.fs b/TestCentre/LibraryTests.fs
index 0678e99..8a2462d 100644
--- a/TestCentre/LibraryTests.fs
+++ b/TestCentre/LibraryTests.fs
@@ -111,6 +111,8 @@
         "reset" function to see all the images produced by this test. This will
         mean you will need to manually delete the images yourself if you do. *)
 
+        // scaleLineThickness
+
         [<Property>]
         let ``Can apply grid to image and save it using BrushSpec`` () =
             resetSavingTestArea ()
@@ -219,6 +221,8 @@
 
     module UnitTests =
 
+        // scaleLineThickness
+
         open TestingHelpers
         open Xunit
         open DeathSocket
@@ -254,4 +258,22 @@
         [<Fact>]
         let ``Divide By Zero Exception is thrown when 0 columns is used when determining vertical lines`` () =
             let result () = GridPainter.determineVerticalLines 100 100 0
+            Assert.Throws<DivideByZeroException>(fun () -> result () |> ignore)
+
+        [<Fact>]
+        let ``Divide By Zero Exception is thrown when previewDimension is set to 0 when calling scaleLineThickness`` () =
+            let result () =
+                GridPainter.scaleLineThickness 0.0 1.0 1.0
+            Assert.Throws<DivideByZeroException>(fun () -> result () |> ignore)
+
+        [<Fact>]
+        let ``Divide By Zero Exception is thrown when actualDimension is set to 0 when calling scaleLineThickness`` () =
+            let result () =
+                GridPainter.scaleLineThickness 1.0 0.0 1.0
+            Assert.Throws<DivideByZeroException>(fun () -> result () |> ignore)
+
+        [<Fact>]
+        let ``Divide By Zero Exception is thrown when lineThickness is set to 0 when calling scaleLineThickness`` () =
+            let result () =
+                GridPainter.scaleLineThickness 1.0 1.0 0.0
             Assert.Throws<DivideByZeroException>(fun () -> result () |> ignore)
\ No newline at end of file