@bdunham7: If using my very recently calibrated 3458A (by Keysight Metrology, Standards Lab Calibration, .3ppm uncertainty), the errors are as follows:
1) 3458A#1: +1.8ppm (Keysight ISO17025 calibrated) (cal date 05/25/2023)
2) 3458A#2: +1.6ppm (Keysight ISO17025 calibrated) (cal date 03/29/2024)
3) 3458A#3: +3.3ppm (ISO17025 calibrated, not by Keysight) (cal date 10/30/2023)
4) 3458A#4: +0.0ppm - the reference meter just returned from Keysight Metrology
The reference meter agrees with the 732A within .3ppm (today's reading was even less). That original measurement was taken by the 3458A 18 months ago when the unit returned from Keysight Metrology.
So, those values were taken after ACAL, NPLC300, leads zeroed out. If you wait 24 hours, things get interesting. Sometimes they drift together, sometimes more apart.
My conclusion: The ISO17025 grade calibration is referencing a Fluke 5730A calibrator in all 3 cases while my reference meter was calibrated by comparison to Keysight's JVS. Of course, YMMV.
Almost forgot to mention the obvious which is that the Fluke 5730A calibrated meters agree within 1.7ppm, the two calibrated at Keysight within 0.2ppm!
Hope this was useful to you.
TomG.