More on SI units



May I contribute some water to the ‘tempest in a teapot’ about SI units. In L K. Coachman in the September 4,1979, EOS, I found a kindred spirit. Other SI units, in addition to pascals, also lack the capability of being visualized and hence more comprehensible.

My work in irrigation is primarily at the application level on the farm. The units of depth are commonly used, e.g. 23 mm of rain, 8 mm per day evapotranspiration, irrigation application of 100 mm, etc. Similarly, it is very practical to use a volume unit that involves depth, so the hectare meter is very logical. It also has many of the advantages of the old acre foot unit. The SI unit for volume is the m3. However, to say to a farmer to apply 7.5 x 103 m3 is rather abstract. To tell him to apply 100 mm on his 7.5 hectare field conveys a visual concept and is very understandable.