Mesa 7i96 to spindle FWD/REV control

Function INTERPXY(Optional ZValues As Range, Optional X As Double, Optional Y As Double, Optional Xaxis As Range, Optional Yaxis As Range) As Double
 
    Dim Xmax, Xmin, Ymax, Ymin, Ystart, q1 As Integer
    Dim V, V1, V2, V3, V4 As Double
    Dim dx, dy As Double
    
    
           
    If Xaxis Is Nothing Then Set Xaxis = ZValues.Resize(RowSize:=1).Offset(RowOffset:=-1)
    If Yaxis Is Nothing Then Set Yaxis = ZValues.Resize(ColumnSize:=1).Offset(ColumnOffset:=-1)

            
' Find X bracket

            Xmax = 0
            Xmin = 1
            Do
                Xmax = Xmax + 1
                If X >= Xaxis(1, Xmax).Value Then Xmin = Xmax
            Loop Until Xmax >= Xaxis.Count Or Xaxis(1, Xmax).Value >= X

            
' Find Y bracket

            Ymin = 1
            Ymax = 0
            Do
                Ymax = Ymax + 1
                If Y >= Yaxis(Ymax, 1).Value Then Ymin = Ymax
            Loop Until Ymax >= Yaxis.Count Or Yaxis(Ymax, 1).Value >= Y
            
' Set 4 corner values
' V1 V2
' V3 V4
            
            V1 = ZValues(Ymin, Xmin).Value
            V2 = ZValues(Ymin, Xmax).Value
            V4 = ZValues(Ymax, Xmax).Value
            V3 = ZValues(Ymax, Xmin).Value
            
            If Xmax <> Xmin Then
            dx = (X - Xaxis(1, Xmin).Value) / (Xaxis(1, Xmax).Value - Xaxis(1, Xmin).Value)
            Else
            dx = 0
            End If
            
            If Ymax <> Ymin Then
            dy = (Y - Yaxis(Ymin, 1).Value) / (Yaxis(Ymax, 1).Value - Yaxis(Ymin, 1).Value)
            Else
            dy = 0
            End If
                        
            INTERPXY = (1 - dx) * (1 - dy) * V1 + dx * (1 - dy) * V2 + (1 - dx) * dy * V3 + dx * dy * V4
    
   
End Function