Private Sub CheckBox1_Click()
If CheckBox1 Then
Worksheets("sheet1").ChartObjects(1).Chart.SeriesCollection(1).Trendlines _
.Add Type:=xlLinear, Name:="Linear Trend", Forward:=[c5]
With Worksheets("sheet1").ChartObjects(1).Chart.SeriesCollection(1).Trendlines(1).Format.Line
.Weight = 2
.ForeColor.RGB = RGB(91, 155, 213)
.DashStyle = 3
End With
Else
Worksheets("sheet1").ChartObjects(1).Chart.SeriesCollection(1) _
.Trendlines(1).Delete
End If
End Sub