Be the change you want to see.

I remember the first time I got those units out of gnu units on the command line scratching my head wondering why I'd never used them before and why it was using them at the same time.

Brewers introduced me to this with hectolitres

Hectolitres and hectograms are used fairly often (the latter, daily) in Italian, for example.

Hectolitre is 100 litres, not 100ml, but hectogram is 100g, not 100kg? Very confusing!

I mean

    Hecto = 100
    Hectoliter = 100 litres
    Hectogram = 100 grams

    Kilo = 1000
    Kiloliter = 1000 litres
    Kilogram = 1000 grams

It doesn't look that confusing?

Well yeah, litres and grams are the base units. Just because 1ml is 1g of water doesn't change how SI prefixes work.

I would have thought if gram is the base unit for weight then millilitre is the base for volume, but I must be wrong

I’m personally partial to attolightyears (about 1cm).

Surely you'd use the base unit of time, the second (lightseconds)?

atto-lightyear = 1e-18 lightyear

lightyear = 3.156e+7 lightsecond

Hence, atto-lightyear = 3.156e-11 lightsecond = 31.56 pico-lightsecond