>>>I've never heard the metric "deca" or "deci", or "hecta" being used at all.
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>>"Deci" is short for deciliter, and it's quite a common measure, for both drinks and recipes. "Dek" is 10g, again used in recipes or when buying food - you buy "20 deks of ham sausage", though "200 grams" is also quite common.
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>Yes I know. We did all those prefixes in school. I'm just saying that I've never seen them used anywhere. If you bought cloth, for ex., you'd buy by the metre, like 6.5 m, never 6 m 50 dekametres. Window blinds are measured in mm, e.g. 1020 mm drop, plasterboard (dry lining?) too, usw.

Oh, that - yes, the rule is that you go by the most significant unit of measure. 6.5 kg would never be pronounced in kilos and dekagrams - except in 3rd grade when the kids are learning the units - it'd be "šest ipo kila" (six anahalf kilos), 3.3m would be "three meters thirty" etc. The people generally abide by your rule of saving syllables.