the.com/gold standard

means The benchmark so widely trusted that everything else gets measured against it.

from Rooted in literal economics: a 19th-century monetary system where a country's currency was directly backed by and convertible into fixed amounts of gold, making gold the fixed reference point of value. Major economies adopted it through the 1800s and it largely unraveled by the mid-20th century, but the phrase outlived the policy — by the 1900s people were already using 'gold standard' figuratively for anything considered the ultimate, trusted measure of quality.