Convert a String to a Unit
as.unit(u, default = list(unit = expression(), scale = ""))A character string indicating a variable name. The following
names are recognized: "DBAR",
"IPTS-68", "ITS-90", "PSS-78", and "UMOL/KG".
All other names yield a return value equal to the value of the
default argument.
A default to be used for the return value, if u
is not a recognized string.
A list with elements unit, an expression,
and scale, a string.
This function is not presently used by any oce functions, and is
provided as a convenience function for users.