> Just because most metric unit ratios are a power of ten doesn’t mean there is no ratio. There is one metric unit for distance (the meter). Likewise, there is

> Just because most metric unit ratios are a power of ten doesn’t mean there is no ratio. There is one metric unit for distance (the meter). Likewise, there is one unit for force (the Newton); one for energy (the Joule); one for mass (the kilogram); one for electric charge (the Coulomb); etc. > You can divide a meter into four 25 centimeter pieces, or five 2 decimeter pieces. The parent specifically asked for "whole numbers". The term "centi" means hundredth, and "deci" means tenth, so your examples are 25/100 metres and 2/10 metres, which are not whole numbers. If we allow fractions (which we should!) then sure, we can make any rational ratio we like. > Just because most metric unit ratios are a power of ten doesn’t mean there is no ratio. All ratios between units in metric/SI are 1, by design. You're probably referencing power-of-ten ratios between prefixes, like "centi", "kilo", "mega", "micro", etc. Those are not units, they're just an alternative way of writing numbers. For example, 2km = 2000m because 2k = 2000 (by definition of k); nothing to do with units, which in both cases are meters. Likewise, both "2 dozen meters" and "24 meters" are in units of meters; the first isn't in a separate unit of "dozen meters". > Alternatively, you could restrict US units to just yards if you wanted I've never seen anyone restrict to using yards; usually the restriction is to feet, like the foot-pound-second system https://en.wikipedia.org/wiki/Foot%E2%80%93pound%E2%80%93second https://en.wikipedia.org/wiki/Foot%E2%80%93pound%E2%80%93sec... > and get nearly the same inconvenient behavior as meters The explicit convenience of using meters (rather than the implicit convenience of not having any length conversions) is that all of its conversion factors to combinations of other units are one, by definition. For example: Pushing a force over a distance takes energy (see https://en.wikipedia.org/wiki/Work_(physics) https://en.wikipedia.org/wiki/Work_(physics) ) so distance = energy / force. In metric, 1 meter = 1 Joule per Newton. In contrast, 1 yard = 0.968 calories per pound-force, which is less convenient. Newton's second law says force = mass × acceleration, so distance = force × time² / mass. In metric, 1 meter = 1 Newton second² per kilogram. In contrast, 1 yard = 2.978 pound-force second² per slug, which is less convenient. etc. I actually wrote a page about this on my blog a while ago http://www.chriswarbo.net/projects/units/metric_red_herring.html http://www.chriswarbo.net/projects/units/metric_red_herring....