Elapsed Time Calculation using Vb.net

This Elapsed Time Calculation System is useful for check the employees working time. This system start to work when employee log in to the office until log off from office.

Import the Following Namespace

Dim date1 As String
Dim i, flg As Integer
Dim th, ot As Decimal
Public st As String
Public wh As Decimal

Create the Function

Private Function CalculateHours(ByRef tm1 As Date, ByRef tm2 As Date) As Decimal
        Dim i, j As Double

        i = Hour(tm2) - Hour(tm1)
        j = (Minute(tm2) - Minute(tm1))

        If j < 0 Then
            i = i - 1
            j = 60 + j
        End If
        CalculateHours = CDec(i & "." & j)
    End Function

Ok Button

Private Sub Button1_Click(sender As Object, e As EventArgs) Handles Button1.Click
        If (CalculateHours(DateTimePicker1.Value, DateTimePicker2.Value) < 0) Then
            MessageBox.Show("Invalid Login / Logout Time", "Error", MessageBoxButtons.OK, MessageBoxIcon.Error)
            Exit Sub
        End If
        Try
            th = 0
            Dim b, fin As Date
            txtOTH.Text = CalculateHours(DateTimePicker1.Value, DateTimePicker2.Value)
            th = (CalculateHours(DateTimePicker1.Value, DateTimePicker2.Value) \ 1 + (((CalculateHours(DateTimePicker1.Value, DateTimePicker2.Value) Mod 1) * 100) / 60))

            st = Today & " " & st.Substring(11)
            b = st

            If CalculateHours(b, DateTimePicker1.Value) > 0 Then
                txtOTH.Text = (CalculateHours(b, DateTimePicker1.Value) \ 1 + ((CalculateHours(b, DateTimePicker1.Value) Mod 1) * 100) / 60)

            End If

            If (Weekday(DateTimePicker3.Value) = 7) Then
                ot = CalculateHours(b.AddHours(5.5), DateTimePicker2.Value)
            Else
                ot = CalculateHours(b.AddHours(wh), DateTimePicker2.Value)
            End If
            txtOTH.Text = ot \ 1 + (((ot Mod 1) * 100) / 60)
            If (Convert.ToDecimal(txtOTH.Text) < 0) Then
                txtOTH.Text = "0.00"
            End If
        Catch ex As Exception

        End Try

    End Sub

i have attached the video link below. which will do this tutorials step by step.