[RESOLVED] Surface Area of a Hollow Cylinder

[toecutter]

I have this so far

       Dim cColumnHeightRound As Double = (40) / 1000
      
        Dim n As Double = 3.142857142 '/ 1000
        rRadius = (70) / 1000 '* 2
        Dim mM2 As Double = 0
        mM2 = (2 * n) * rRadius * cColumnHeightRound
        'mM2 = mM2 / 1000
        'mM2 = Math.Round(mM2, 3)
        Me.txtTotalM2Round.Text = mM2.ToString

The result is 0.0175999999952 which is incorrect.

No matter what i try i can not get it to be 0.175 which is correct i believe.

regards
toe

edit

 Dim cColumnHeightRound As Decimal = Decimal.Parse(Me.cmbColumnHeightRound.Text)
        rRadius = Decimal.Parse(Me.txtRadius.Text)
        Dim mM2 As Decimal = 0
        mM2 = CDec((2 * Math.PI) * rRadius * cColumnHeightRound)
        mM2 = Math.Round(mM2, 3)
        mM2 = mM2 / 1000
        mM2 = Math.Round(mM2, 3)
        Me.txtTotalM2Round.Text = mM2.ToString

seems to be ok :blush

help, after a closer look its incorrect