Find SI prefix for unit
find_prefix(x, f = min, minexp = -Inf, maxexp = Inf, mu = TRUE)
a numeric
minimum (decimal) exponent to consider, e.g. -3 to suppress prefixes smaller than milli (m).
maximum (decimal) exponent to consider, e.g. 3 to suppress prefixes larger than kilo (k).
if TRUE
, should a proper mu be used for micro, otherwise use
u as ASCII-compatible replacement
character with the SI prefix