[halper]

Yes, you are correct. As the SI brochure states: "Compound prefix symbols, i.e. prefix symbols formed by the juxtaposition of two or more prefix symbols, are not permitted."

Unfortunately, almost no one uses SI units and/or prefixes correctly.

[taffydavid]

I have another alternative: you could simply prefix the km with ,000

[AngryData]

Meh, units should be used at the convenience of us, they are all arbitrarily defined to start with. We still use lots of non-si units, like AUs, minutes seconds and hours, degrees and arc units, or whatever else. Conversion is easier than ever today so I think units should be adapted to the application and use more fractional units when appropriate.