private void btnExport_Click(object sender, EventArgs e)
{
SaveFileDialog sfd = new SaveFileDialog();
sfd.DefaultExt = "csv";
sfd.Filter = "Comma-separated value (*.csv)|*.csv|All files (*.*)|*.*";
if (sfd.ShowDialog() != System.Windows.Forms.DialogResult.OK)
return;
ExportCharts(sfd.FileName);
MessageBox.Show("Chart data exported");
}