If I understand the question correctly -- why did I suggest commodity= for a measurement of height but not for weight -- it's not a novice question at all. My thinking (which may be muddled by lack of sleep) is that for weight, we don't normally express the commodity, which is really "person". But because with weight or mass there really can only be one measurement for a person (leaving aside all sorts of nuances like being weighed in the morning vs evening, with vs without clothes, etc.), I felt, perhaps incorrectly so, that it was OK to let that bit of information be implied by the fact that the entire table of data is about people. In truth, when measuring height, the commodity is still "person". But for the height, unlike weight, the unit does not tell you what direction you're measuring. The unit measures distance, which could be height, width, depth, or circumference. So I thought in this case it was better to supply the information explicitly. Perhaps it should be on type= instead. Enough babble. Time for sleep. G'night.