Smaller units?

I think adding these smaller units is kind of a batch job or more or less simple. It just needs to be done and yes, it makes sense, as we should not assume the use-cases.

Would be great if someone could implement a MR for that.

Hi , I have added mili-grams and micro-gram units.
Could please review it.
Let me know if you need some more changes.

Thankyou !!

Done few nitpicks ~~ changes looks good, hence marking this RTBC

Its adding "WeightUnit" (mg, µg) to "LengthUnit" . May need to fix.