private void cbULPrefix_SelectedValueChanged(object sender, EventArgs e)
{
if (edtULValue.Quantity == null)
edtULValue.Quantity = new Quantity();
if (edtULValue.Quantity.Unit == null)
edtULValue.Quantity.Unit = new StandardUnit();
edtULValue.Quantity.Unit.Prefix = cbULPrefix.SelectedValue as string;
}