The metric system was officially introduced by a law passed on December 17, 1923.  However, old Thai units are still in common use, especially for measurements of land which is often quoted using the traditional Thai system of waa, ngaan and rai. Old-timers in the provinces will occasionally use the traditional Thai system of weights and measures in speech, as will boat-builders, carpenters and other craftsmen when talking about their work. Here are some conversions to use for such occasions: