public static String Evaluate(MercatorUi.MovableControls.MovableExpression currentExpression)
{
    // enter your customized code here

    MercatorUi.Forms.Billing.BillingForm billingForm = (MercatorUi.Forms.Billing.BillingForm)currentExpression.Form;

    return "Article = " + billingForm.CurrentRowCellValue("id_article")
        + " | PU = " + billingForm.CurrentRowCellValue("pu")
        + " | Q = " + billingForm.CurrentRowCellValue("q")
        + " | Dispo = " + billingForm.CurrentRowCellValue("DISPO.DISPO")
        + " | Q * 2 = " + billingForm.CurrentRowCellValue("q * 2")
        + " | CLE = " + (billingForm.CurrentRowCellValue("id_article") != "" ? billingForm.BillingEngine.StockRecords[billingForm.CurrentRowCellValue("id_article")]?.S_CLE3 ?? "" : "");
}