From Wet Markets to Laboratories: Why Metrological Standards Can Never Be Absolutely Uniform

Have you ever had this experience? You buy half a kilogram of apples at a wet market, weigh them on your scale at home, and find they are 25 grams short. You fill up 50 liters of gasoline at a gas station, always feeling the meter ticks faster than your wallet drains. Even on the same physical examination device, your blood pressure readings differ between morning and afternoon. Behind these seemingly “dishonest” or “inaccurate” incidents lies a deeper truth — metrological standards have never been, and can never be, absolutely uniform. Most common metrological disputes in daily life are not caused by merchants deliberately shortchanging customers, but by inherent “discrepancies” within the standards themselves.

The Battle Between Kilograms and Jin at Wet Markets

In April 2025, a dispute broke out in the ancient town of Dali, Yunnan. A tourist placed his 170-gram iPhone on a vendor’s scale, and the reading showed 0.34 kilograms. Seemingly accurate, yet the tourist felt cheated. Where was the problem?

The answer lies in differing customary units of measurement. Many regions in Yunnan still retain the traditional use of jin (Chinese catty). The “one jin” mentioned by the vendor refers to 500 grams, while the scale displays values in kilograms. The same word “jin” means different weights to different people. No one is at fault here; it is a collision of historically inherited measurement habits in the same space.

The metric system originated during the French Revolution, born out of the Enlightenment ideal of “unifying the world by natural laws”. More than two hundred years later, however, numerous countries and regions still retain traditional units of measurement to varying degrees:

• The United States is one of the few developed nations that still widely uses imperial units — miles, pounds and degrees Fahrenheit are deeply embedded in every aspect of social life. The US attempted metrication in the 1970s, but the effort fizzled out due to excessive costs and public resistance.
• In China, the legal measurement system is metric, yet traditional units such as jin, mu and cun remain widely used among the public.

These differences are not signs of backwardness; they form part of cultural identity. When a unit of measurement carries the life memories of generations, replacing it involves far more than just swapping out a few scales.

The story of metrological standards is, at its core, a story of “ideal versus reality”. Ideally, the whole world would adopt one set of units, one measuring stick and one standard, facilitating smooth trade and communication and aligning with scientific principles. In reality, history carries inertia, technology has limits, economic costs exist, and industries have unique characteristics. Combined, these factors determine that metrological standards can only achieve relative uniformity, never absolute consistency.

With this understanding, we may view daily metrological puzzles with greater empathy. A few grams of deviation on a market scale does not always mean a dishonest vendor — it may simply be the inherent accuracy class of that scale. Inconsistent test results between two hospitals do not necessarily mean misdiagnosis; the traceability chains of their testing systems may differ. Crude oil is traded by the barrel internationally while domestic fuel is sold by the liter, not to create confusion intentionally, but as a result of historical path dependence.

The imperfection of metrological standards mirrors the complexity of our world. What we can do is not demand absolute uniformity, but establish mutual recognition amid differences and seek consensus amid diversity — much like human civilization itself, integrating through collisions and advancing amid divergences.