I just want to add, that this parameter for me is the most important one, for such instruments like the 3458A, the Fluke 720A and the 752A. Latter ones are explicitely called "Transfer Standards", and therefore you see, that this parameter has to be well defined, and not being "fuzzy". The transfer accuracy is always mixed with the linearity (where I come back to my problem of definition) Such real "Autocal" instruments (plus Fluke 5440, 5720) simply "live" from their own capability of making ultra precise transfers Outstanding are the 3458A and the 5720A, because they not only do transfers within a single mode by their linearity (i.e. auto-calibrating all DCV ranges), but also to different modes (ACV, ACI, DCI) by ultra precise converters (mainly AC/DC). Here you have to specify also the transfer accuracy of the conversion method. Frank