Well, the 5440/5442 is in fact an artifact calibration (AUTOCAL) instrument, with some limitations:
- 0.1ppm resolution (of gain shift)
- small gain shifts only
- ranges 11V, 22V, 250V and 1100V only (cannot autocal 2.2V and 220mV ranges)
Fluke did not yet (at about 1986) call it clearly an artifact calibration instrument, maybe because they were not self-confident about this, and as the conservative metrology community would have grilled them.
When they introduced the artifact calibration with the 5700A, (early 1990-ties) they initially had a lot of trouble to be accepted by the NBS, and others, and a lot of additional verification had to be performed, before this 57xxA series became the artifact instrument standards, as of to-day.
The 3458A ACAL was accepted much easier, as somebody reported here, due to the close cooperation of NBS and HP on the JJ array research.
Anyhow, if you read the service manual very carefully, especially paragraph 3-27, 3-28 about internal / external calibration, and the appendix "Recent innovations in DCV calibrator design", page A-11, it's quite evident, that the 544x acts exactly as an artifact instrument. (In fact the manuals are quite odd to read, it took me a while to discover this fact, between the lines, or out of what is NOT said)
One decisive hint is, that during calibration, you can always omit the complete external calibration, of course except the 10V calibration, that is the 10V (ext) to 13V (int) transfer.
After this initial step, you are allowed to take the short cut, and only do the internal calibration, for the above mentioned 4 higher ranges, w/o any specified penalty.
So up to this point, you only need an external 10V reference, but no 752A.
In the whole manual there is no restriction for that abbreviated procedure, so it should bring all ranges to their 24h limits, provided the internal 13V reference is still in cal.
Maybe, if the internal resistors had drifted too much, these small correction gain factors would get too big, and a complete external calibration would be necessary.
But as old instruments probably do not drift that much any more, this does also not occur. (Never got an internal cal error the last 7 years..)
Maybe also, that an extensive external calibration would provide greater resolution than 0.1ppm (see A-11), but this is not relevant for an ~0.5ppm grade instrument.
The internal/external cal uncertainty is also not clearly specified for neither case, and the Fluke 752A also provides 0.2 and 0.5ppm transfer uncertainties only.
The 5440B and the 57x0A both have a similar internal transfer / ACAL system inside, especially both have ovenized divider resistors.
This allows precise gain calibration of all DCV ranges, at low bridge excitation voltages, even for the High Voltage ranges.
Hint @ zlymex: the 5440B has no design flaw in this sense at all, because the temperature of the divider resistors is always constant, either with the 1000V burden (30sec stabilization required), or with the -13V bridge configuration. Other HV effects can be neglected, I think. Also, if that would be a design flaw, the 57xx instruments would have the very same, which is accepted to not be the case.
Also, the 752A is calibrated at 20V level, even for the 100:1 / 1kV range, generating exceptional uncertainty, by T.C. matching, instead of ovenizing.
The 544x is even superior over the 57xx, as it uses the Hamon configuration, which is more precise (like the 752A) than the A/D or D/A dependent 10:1 transfers inside the 3458A (~0.3ppm) and the 57xx (< 1ppm

).
The 544x is superior over the 3458A at least in the 1000V range, as the 3458A lacks all kind of thermal compensation methods.
I also have compared the internal calibration function of my 5442A, against the 3458A and my Hamon type 100:1, 10:1 divider, and never found a contradiction to the assumed artifact calibration functionality of the 5442B.
All three agree always within about typ. 0.2ppm, whereas the 3458A is off by about -3ppm at 1000V, compared to the other instruments.
As a conclusion, the 544xB is definitely an artifact predecessor of the accepted 57xx instruments, but FLUKE maneuvered verbally around that fact, these days.
Frank
PS for e61_phil: Like all other ACAL instruments, this internal calibration is necessary once a day, at least, to compensate for short termed drifts.
Also, you interpreted my statements on amplifier.cd correctly, I think, maybe the German text is even more precise.