How to change missing_value of NaN?

[Mark A Ohrenschall <Mark.A.Ohrenschall@xxxxxxxx>]

I'm trying to use the missing function in ferret to change a missing_value
of NaN to something like -9999.

ncdump shows the missing_value attribute as:

                depth:missing_value = -1.e+34f ;
and this is what I'm trying in ferret:
yes? use/order=x-y gulf4.nc
yes? set memory/size=525
 Cached data cleared from memory
yes? let dem=missing(depth,-9999)
yes? save/file=dem.nc dem
 LISTing to file dem.nc
yes?
However, dem.nc retains the missing_value of NaN (in the data as well as
the attribute).

Incidentally, ncatted doesn't change the missing_value either. Do I need to express the missing_value attribute differently, e.g., "NaNf"?

Thanks,

Mark