|Note : Alternative definitions of the SI prefixes and their symbols are
|not permitted. For example, it is unacceptable to use kilo (k) to
|represent 2^10 = 1024, mega (M) to represent 2^20 = 1 048 576, or giga
|(G) to represent 2^30 = 1 073 741 824.

Table 5. SI prefixes

Factor      Prefix        Symbol
------  ----------------- ------
10^-6  = (10^3)^-2  micro  ?

Is there any official standard which permits usefulness of a lowercase
"u" in character sets where the "mu" is not available?  Certainly, there
is no linguistic relationship between the characters, but the "u" is the
one that looks most like a "mu" and I've seen it used for that purpose
an awful lot...