> You can have centimetres but that not in the spirit of the metric system really.
"Centi" is an SI prefix just as much as "kilo" is, and has been part of the metric system since 1795 just like "kilo". I don't see how it's "not in the spirit" of the metric system. It also fits in neatly in that 1cm^3 of water is roughly 1 gram (the original provisional definition of gram was 1cm^3 of water at the melting point of ice; the current definition is more precise), and so 10cm^3 of water is roughly 1 liter.
The SI system has prefixes going up and down one power of 10 up to 10^3 and down to 10^-3, and then in steps of 10^3. They're all equally part of the system; some are just more common in some contexts that others (e.g. we use hectograms but rarely hectolitres, and decilitres but rarely decimetres, and centimetres and centilitres but rarely centigrams) depending on what happens to be convenient.
E.g. kilo(10^3), hecto(10^2), deca(10^1), deci(10^-1), centi(10^-2), milli(10^3), but then mega (10^6) and micro(10^-6) are the next steps.
"Centi" is an SI prefix just as much as "kilo" is, and has been part of the metric system since 1795 just like "kilo". I don't see how it's "not in the spirit" of the metric system. It also fits in neatly in that 1cm^3 of water is roughly 1 gram (the original provisional definition of gram was 1cm^3 of water at the melting point of ice; the current definition is more precise), and so 10cm^3 of water is roughly 1 liter.
The SI system has prefixes going up and down one power of 10 up to 10^3 and down to 10^-3, and then in steps of 10^3. They're all equally part of the system; some are just more common in some contexts that others (e.g. we use hectograms but rarely hectolitres, and decilitres but rarely decimetres, and centimetres and centilitres but rarely centigrams) depending on what happens to be convenient.
E.g. kilo(10^3), hecto(10^2), deca(10^1), deci(10^-1), centi(10^-2), milli(10^3), but then mega (10^6) and micro(10^-6) are the next steps.