Задать коэффициент единицы измерения из свойства элемента

 if(CModule::IncludeModule('catalog') && CModule::IncludeModule('iblock')){

            $get = CIBlockElement::GetList(array(),array('IDLOCK_ID' => 18, 'ID' => 118962),false,false,array("ID", "IBLOCK_ID",'PROPERTY_520'));
            if($list = $get->GetNext());
            $quant = $list['PROPERTY_520_VALUE'];
If (!empty($quant)){
echo $quant;


            $res = CIBlockElement::GetByID(118962);

            if($ar_res = $res->GetNext())
            { $IBLOCK_ID = $ar_res['IBLOCK_ID'];}

            if($IBLOCK_ID==18) {

                $db_measure = CCatalogMeasureRatio::getList(array(), $arFilter = array('PRODUCT_ID' => 118962), false, false);
                while ($ar_measure = $db_measure->Fetch()) {
                    $new_measure = CCatalogMeasureRatio::update($ar_measure['ID'], array("PRODUCT_ID" => 118962, "RATIO" => $quant));
                }
                }
            }

        }

 array("PRODUCT_ID" => $productid, "RATIO" => 2)