Пример обновление коэффициентов MeasureRatio

$eventManager->addEventHandler("catalog", "\Bitrix\Catalog\MeasureRatio::OnBeforeUpdate", function (\Bitrix\Main\Event $event) {
     $result = new \Bitrix\Main\Entity\EventResult;
     $data = $event->getParameter("fields");
     $arSelect = Array("ID","IBLOCK_ID", "PROPERTY_KOEFFITSIENT_FASOVKI");
     $arFilter = Array("ID" => $data["PRODUCT_ID"]);
     $res = CIBlockElement::GetList(Array(), $arFilter, false, Array("nPageSize"=>50), $arSelect);
     while($ob = $res->GetNextElement())
     {
         $arFields = $ob->GetProperties();
     }
     if ($arFields['KOEFFITSIENT_FASOVKI']['VALUE'] == '0' || empty($arFields['KOEFFITSIENT_FASOVKI']['VALUE'])) {
         $result->modifyFields(array('RATIO' => 1));
         AddMessage2Log('Ноль или пусто  -  Товар ' . $data["PRODUCT_ID"]);
     } else {
         $true_coef = str_replace(',','.',$arFields['KOEFFITSIENT_FASOVKI']['VALUE']);
         $result->modifyFields(array('RATIO' => $true_coef));
         AddMessage2Log($true_coef . ' Товар ' . $data["PRODUCT_ID"]);
     }
     return $result;
 });