The length of an NDF character component (i.e. the number of characters it contains) is determined by the last assignment made to it, e.g. by NDF_CPUT, and may be obtained using the routine NDF_CLEN. For instance:
INTEGER LENGTH
...
CALL NDF_CLEN( INDF, 'Units', LENGTH, STATUS )
will return the number of characters in the units component via the LENGTH argument. If the specified component is undefined, then a value of zero will be returned.