diff --git a/GsaGH/Parameters/0_Model/GsaGridLine.cs b/GsaGH/Parameters/0_Model/GsaGridLine.cs
index a0a92b4b7..bfb0e5900 100644
--- a/GsaGH/Parameters/0_Model/GsaGridLine.cs
+++ b/GsaGH/Parameters/0_Model/GsaGridLine.cs
@@ -35,6 +35,7 @@ public GsaGridLine(Arc arc, string label = "") {
       if (arc.Plane.ZAxis.Z < 0) {
         arc = new Arc(arc.EndPoint, arc.MidPoint, arc.StartPoint);
       }
+
       Curve = new PolyCurve();
       Curve.Append(arc);
 
@@ -60,12 +61,19 @@ public GsaGridLine(Arc arc, string label = "") {
     }
 
     public GsaGridLine(Line line, string label = "") {
+      bool IsCounterClockwise =  Vector3d.CrossProduct(Vector3d.XAxis, line.UnitTangent).Z >= 0;
+      double radians = Vector3d.VectorAngle(Vector3d.XAxis, line.UnitTangent);
+      double vectorAngle = RadiansToDegrees(radians);
+      if (!IsCounterClockwise) {
+        vectorAngle = 360 - vectorAngle;
+      }
+
       GridLine = new GridLine(label) {
         Shape = GridLineShape.Line,
         X = line.From.X,
         Y = line.From.Y,
         Length = line.Length,
-        Theta1 = Vector3d.VectorAngle(new Vector3d(1, 0, 0), line.UnitTangent) * 180 / Math.PI
+        Theta1 = vectorAngle
       };
       Curve = new PolyCurve();
       Curve.Append(line);
@@ -73,6 +81,11 @@ public GsaGridLine(Line line, string label = "") {
       UpdatePreview();
     }
 
+    private static double RadiansToDegrees(double radians)
+    {
+      return radians * 180 / Math.PI;
+    }
+
     internal static Arc ToArc(GridLine gridLine) {
       var center = new Point3d(gridLine.X, gridLine.Y, 0);
       double angleRadians = (gridLine.Theta2 - gridLine.Theta1) * Math.PI / 180.0;
@@ -93,6 +106,7 @@ internal static PolyCurve ToCurve(GridLine gridLine) {
         Arc arc = ToArc(gridLine);
         curve.Append(arc);
       }
+
       return curve;
     }
 
@@ -126,8 +140,8 @@ public GsaGridLine(GsaGridLine other) {
     public override string ToString() {
       string label = GridLine.Label != "" ? $"{GridLine.Label} " : string.Empty;
       string type = GridLine.Shape == GridLineShape.Arc ? "Shape: Arc " : string.Empty;
-      string s = $"{label}{type}X:{GridLine.X} Y:{GridLine.Y} Length:" +
-        $"{GridLine.Length} Orientation:{GridLine.Theta1}°";
+      string s = $"{label}{type}X:{GridLine.X} Y:{GridLine.Y} Length:"
+        + $"{GridLine.Length} Orientation:{GridLine.Theta1}°";
       if (GridLine.Shape == GridLineShape.Arc) {
         s.Replace("Orientation", "Theta1");
         s += " Theta2:" + GridLine.Theta2 + "°";
@@ -147,8 +161,12 @@ internal void UpdatePreview() {
       if (segment == null) {
         return;
       }
+
       if (Curve.IsLinear()) {
-        Points = new Point3d[2] { segment.PointAtStart, segment.PointAtEnd };
+        Points = new Point3d[2] {
+          segment.PointAtStart,
+          segment.PointAtEnd
+        };
       } else {
         Points = segment.DivideEquidistant(segment.GetLength() / 360.0);
       }
diff --git a/GsaGHTests/3_Components/0_Model/GsaGridLineTests.cs b/GsaGHTests/3_Components/0_Model/GsaGridLineTests.cs
new file mode 100644
index 000000000..9be5d0a4e
--- /dev/null
+++ b/GsaGHTests/3_Components/0_Model/GsaGridLineTests.cs
@@ -0,0 +1,44 @@
+using GsaGH.Parameters;
+
+using Rhino.Geometry;
+
+using Xunit;
+
+namespace GsaGHTests.Model {
+  [Collection("GrasshopperFixture collection")]
+  public class GsaGridLineTests {
+
+    [Fact]
+    public void ShouldReturnZeroForParallelLine() {
+      var line = new Line(Point3d.Origin, new Point3d(1, 0, 0));
+      var gsaGridLine = new GsaGridLine(line, string.Empty);
+
+      Assert.Equal(0, gsaGridLine.GridLine.Theta1, precision: 5);
+    }
+
+    [Fact]
+    public void ShouldCalculateAngleBetweenXAxisAndLine() {
+      var line = new Line(Point3d.Origin, new Point3d(1, 1, 0));
+      var gsaGridLine = new GsaGridLine(line, string.Empty);
+
+      Assert.Equal(45, gsaGridLine.GridLine.Theta1, precision: 5);
+    }
+
+    [Fact]
+    public void ShouldProvideTheClockwiseAngle() {
+      var line = new Line(Point3d.Origin, new Point3d(1, -1, 0));
+      var gsaGridLine = new GsaGridLine(line, string.Empty);
+
+      Assert.Equal(315, gsaGridLine.GridLine.Theta1, precision: 5);
+    }
+
+    [Fact]
+    public void ShouldProvideTheClockwiseAngle2() {
+      var line = new Line(Point3d.Origin, new Point3d(-1, -1, 0));
+      var gsaGridLine = new GsaGridLine(line, string.Empty);
+
+      Assert.Equal(225, gsaGridLine.GridLine.Theta1, precision: 5);
+    }
+
+  }
+}