What circumstances during the French Revolution permitted the metric system to gain a foothold?

The trade was difficult with the old system.

Explanation:

The existing system for the measurement of goods did not work well in the trade because there are different system used by the people of different cities so metric system was used in the whole country in place of the old system of measurement during the French Revolution in order to make the trade easier and quick across the country. This metric system is extensively used in the trade as compared to the old system of measurement due to its easiness and fast.

the product of the pressure and volume is also constant