IIW Subcommission II-C have conducted a round robin of ferrite measurements in nominally austenitic stainless steel weld metals, and in duplex ferritic-austenitic stainless steel weld metals, to determine interlaboratory reproducibility of measurement after calibration of shop and field instruments by means of new IIW ferrite secondary standards. The reproducibility, characterised by Percent Variability, is found in general to be no worse than plus or minus 14% of the interlaboratory average FN observed on each of thirteen 'unknown' weld samples.