IEC 646 and the National Replacement Character Set is closely related except with the Dutch variant.
It is closely related to ISO 646, being based on a similar invariant subset of ASCII, differing in retaining $ as invariant but not _ (although most NRCS variants retain the _, and hence comply with the ISO 646 invariant set). Most NRCS variants are closely related to corresponding national ISO 646 variants where they exist, with the exception of the Dutch variant. 
