Problem when obtaining value from a variable VB.net

veran I have a function that is responsible for moving a linear motor, for this I compare two values and if they are equal, the movement function is executed.

While contador1 <= total1

    MsgBox("")

    If slide1 = desde Then
        TrySetTarget(0, hasta)
        System.Threading.Thread.Sleep(1)
    End If

    If slide1 = hasta Then
        TrySetTarget(0, desde)
        System.Threading.Thread.Sleep(1)
        contador1 = contador1 + 1
        If TextBox15.Text <= 1 Then
            contador1 = contador1 + 2
            TextBox15.Text = TextBox15.Text - 1
        Else
            System.Threading.Thread.Sleep(1)
            TextBox15.Text = TextBox15.Text - 1

        End If
    End If




End While

The function above is responsible for moving the engine and this:

Sub TryGetVariables()

    Dim a As String
    Dim b As String
    Dim c As String


    Dim gf1 As String
    Dim gt1 As String
    Try
        Using device As Usc = connectToDevice() ' Find a device and temporarily connect.


            device.getVariables(st1)


            galfaf1 = st1(1).position
            galfat1 = st1(2).position


            slide1 = st1(0).position
            valor = Me.slide1

            a = (5 * galfaf1) / 1023
            b = (5 * galfat1) / 1023


            c = 0.1 * (slide1 / 4 - 1000)



            If a >= 0 And a <= 0.1 Then
                gf1 = 19.23 * a
                'MsgBox(gf1)
                TextBox5.Text = gf1
            ElseIf a > 0.1 And a <= 1.3 Then
                gf1 = 19.23 * a + 25
                'MsgBox(gf1)
                TextBox5.Text = gf1
            ElseIf a > 1.3 And a <= 2.5 Then
                gf1 = 225 * (a - 1.3) + 50
                'MsgBox(gf1)
                TextBox5.Text = gf1
            ElseIf a > 2.5 And a <= 3.4 Then
                gf1 = 755.5 * (a - 2.5) + 320
                'MsgBox(gf1)
                TextBox5.Text = gf1
            End If

            If b >= 0 And b <= 0.1 Then
                gt1 = 19.23 * b
                TextBox12.Text = gt1
            ElseIf b > 0.1 And b <= 1.3 Then
                gt1 = 19.23 * b + 25
                TextBox12.Text = gt1
            ElseIf b > 1.3 And b <= 2.5 Then
                gt1 = 225 * (b - 1.3) + 50
                TextBox12.Text = gt1
            ElseIf b > 2.5 And b <= 3.4 Then
                gt1 = 755.5 * (b - 2.5) + 320
                TextBox12.Text = gt1
            End If

            TrackBar1.Value = c


            ' device.Dispose() is called automatically when the "Using" block ends,
            ' allowing other functions and processes to use the device.
        End Using
    Catch exception As Exception  ' Handle exceptions by displaying them to the user.
        displayException(exception)
    End Try
End Sub

The TryGetVariables () function is executed by means of a Timer every 50 milliseconds and slider1, the variable that gives me problems is refreshed in it, my problem is that when I use it in the code above it does not obtain value and only when I put an MsgBox, it gets value and the engine moves, I tried everything, placing the function within the first code chunk and not using the Timer but it does not work properly because it does not perform all the code's functionality. I do not know what to do, no matter how much I think about it, please appreciate your help.