Define the default symbol for the imaginary unit, that is, the square root of negative one. The default Unicode codepoint for the imaginary unit. (DOUBLE-STRUCK ITALIC SMALL I)
\u2148 := <<IMAGINARY_UNIT>>
Also used for the imaginary unit (especially by electrical engineers, who use "i" to indicate current. (DOUBLE-STRUCK ITALIC SMALL J)
\u2149 := <<IMAGINARY_UNIT>>
Redefine the letter "i" to also be the imaginary unit
i := \u2148
Hm, is there an archive of old versions of units.dat anywhere? Occasionally units get deleted from it - I used to keep old versions but I'd forgotten about this some time ago and haven't done so in a while. (Also that was several hard drive crashes ago so I no longer have the copies I made.)
On the kilogram: "I dislike having a prefixed unit as the base reference. What a horrible decision. Why don't you just have it go to ten and make ten a little louder?"
Some pure gold buried in there. For instance search for candela.