Traditional Units That Refuse to Disappear

Metrication rarely wipes out older units entirely. Instead, legislators fix them to exact metric values, and they live on wherever habits are strongest. Japan made the metric system its sole legal system in most fields in 1959, yet apartments are still advertised by the tsubo of about 3.306 square metres, and pearls are still graded by the monme of 3.75 grams.

In China the market system of 1929 set the jin at half a kilogram and the li at 500 metres, round numbers that made the traditional names easy to keep. The jin remains the everyday unit at food markets. In Hong Kong the catty kept its older value, legally 604.78982 grams, and the gold trade still deals in taels.

Across South Asia and the Gulf, gold is bought and sold by the tola, which British India fixed at 180 grains, about 11.66 grams. The ten-tola bar is a standard product even in countries that are fully metric for all other purposes.

Western examples abound too. Britons give body weight in stones of 14 pounds, horses are measured in hands of four inches, and kettlebells are still sized in Russian poods of about 16 kilograms. Even aviation, almost everywhere metric on the ground, measures altitude in feet and speed in knots.