Calculating Angle Variation

Hi all,

It's been a while since I've posted as I started a new job using AutoCAD but by showing the power of CorelDraws API to my new employer I am back again!... with more questions!

I've Hit a block with probably a quite simple (but fun) problem but for the life of me an elegant and robust solution eludes me!

In short I want to analyse the a curve, recording the perpendicular angle at a series of points along it.

Then give each recorded point a value between 0-180 based on how much it deviates from my target angle. 

Currently It only works correctly when the angle is 0, please see below for the stripped down block of code and an image of its current output to get things moving.

All suggestions and ideas welcome. 

Thanks in advance

Sub PerpLines()
ActiveDocument.Unit = cdrMillimeter
Dim S As Shape
Set S = ActiveShape
Dim Sp As SubPath
Set Sp = S.Curve.SubPaths.First
Dim P As Shape
Dim L As Long: L = 1
Dim step As Long: step = 10
Dim curLength As Double: curLength = 0
Dim sLength As Double: sLength = Sp.Length
Dim X As Double, Y As Double, A As Double
Dim R As Double
Dim targA As Double: targA = 90
Dim aDif As Double
Do While curLength < sLength - step
curLength = curLength + step
Sp.GetPointPositionAt X, Y, curLength, cdrAbsoluteSegmentOffset
A = Sp.GetPerpendicularAt(curLength, cdrAbsoluteSegmentOffset)
Set P = ActiveLayer.CreateLineSegment(X, Y, X + step, Y)
P.Outline.EndArrow = ArrowHeads(1)
P.Outline.Width = 1
P.SetRotationCenter X, Y
P.Rotate A

If A < 0 Then
aDif = A + 360
Else
aDif = A
End If
R = (255) * (Abs(A) / 180)
P.Outline.Color.RGBAssign CLng(R), 50, 50
P.Name = CStr(aDif)
L = L + 1
Set P = Nothing
Loop

End Sub