draw string in center of a rectangle

[user20]

My form has a picturebox that draw a shape with mouse down and up.

my problem is the location of text"020"! I want to draw it in center of rectangle.
please guide me. my codes are:

Imports System.Drawing.Drawing2D

Public Class Form4

    Private NewSegment As Segment
    Private Segments As New List(Of Segment)
    Private Sub PictureBox1_MouseDown(sender As Object, e As MouseEventArgs) Handles PictureBox1.MouseDown

        NewSegment = New Segment(e.Location, e.Location)
        Segments.Add(NewSegment)
        PictureBox1.Invalidate()
    End Sub

    Private Sub PictureBox1_MouseMove(sender As Object, e As MouseEventArgs) Handles PictureBox1.MouseMove
        If NewSegment Is Nothing Then Return
        NewSegment.Point2 = e.Location
        PictureBox1.Invalidate()
    End Sub

    Private Sub PictureBox1_MouseUp(sender As Object, e As MouseEventArgs) Handles PictureBox1.MouseUp
        NewSegment = Nothing
        PictureBox1.Invalidate()
    End Sub

    Private Sub PictureBox1_Paint(sender As Object, e As PaintEventArgs) Handles PictureBox1.Paint
        e.Graphics.SmoothingMode = Drawing2D.SmoothingMode.AntiAlias
        For Each segment As Segment In Segments
            segment.Draw(e.Graphics, Nothing)
        Next
    End Sub
End Class

Class Segment
    Private Const RADIUS As Integer = 15
    Private Shared rc_r As New Rectangle(New Point(-RADIUS, -RADIUS), New Size(RADIUS * 1.5, RADIUS * 1.5)) 'for rectangle
    Private pt1, pt2 As Point
    Private angle As Double = 0
    Private length As Double = 0
    Private Shared pen1 As New Pen(Color.Black, 1.5)
    Private Shared drawFontF As New Font("times new roman", 8, style:=FontStyle.Bold)
    Private Shared SF As StringFormat
    Public Sub New(startPoint As Point, endPoint As Point)
        Point1 = startPoint
        Point2 = endPoint
    End Sub

    Public Property Point1 As Point
        Get
            Return pt1
        End Get
        Set(value As Point)
            pt1 = value
            UpdateAngleAndLength()
        End Set
    End Property

    Public Property Point2 As Point
        Get
            Return pt2
        End Get
        Set(value As Point)
            pt2 = value
            UpdateAngleAndLength()
        End Set
    End Property

    Private Sub UpdateAngleAndLength()
        angle = Math.Atan2(Point2.Y - Point1.Y, Point2.X - Point1.X) * 180.0 / Math.PI
        length = Math.Sqrt(Math.Pow(Point2.X - Point1.X, 2) + Math.Pow(Point2.Y - Point1.Y, 2))
    End Sub
    Public Sub Draw(gr As System.Drawing.Graphics, R As Rectangle)

        If Point1 = Point2 Then Return
        ' save the current state of the graphics
        Dim curState As GraphicsState = gr.Save()

        ' move the origin to the start point of the line
        gr.TranslateTransform(Point1.X, Point1.Y)
        ' rotate the whole surface
        gr.RotateTransform(angle)

        ' draw the line on the x-axis
        gr.DrawLine(pen1, 0, 0, CInt(length), 0)

        ' move the origin along the x-axis to where the center of the circle should be
        gr.TranslateTransform(length + RADIUS, 0)
        gr.DrawRectangle(pen1, rc_r) ' for rectangle

        ' orient back to the "normal" so the 90 is upright
        gr.RotateTransform(-angle)
        ' draw the 90
        Dim rcS As New Rectangle(New Point(-RADIUS, -RADIUS), New Size(RADIUS * 1.5, RADIUS * 1.5))

        gr.DrawString("020", drawFontF, Brushes.DimGray, rcS, SF)

        gr.Restore(curState)
    End Sub
End Class

how change 'RCS' ?