Engineering form of written numbers only uses powers of three, and the relivant SI prefix. Of theses there is the postfix and infix styles. postfix may be more common, but the infix style appears frequently on electronic components.
Here are two functions, eng_form_infix and eng_form_postfix, to convert a number into engeneering form with ether the si symbol as the infix (instead of the '.') or as a postfix. The precision of the conversion is as requested.or type one in below:
View page source to see how it works.