These days many I see many websites shortening large numbers with the metric prefixes, for example Twitter does it like this:
replacing 35 400 with 35.4K, and 34 700 000 with 34.7M. One might also write the current year as 2k17 (though I don't understand what's the point of this as it doesn't save any letters).
Am I also allowed to use the same principle for shortening small quantities with the corresponding metric prefixes, like 0.0042 with 4.2m (m for milli) or 0.0000042 with 4.2μ (μ for micro)?
I'm primarily asking for the technical and scientific fields, but if you can also elaborate on usage in everyday life, this would be a nice addition.