Thanks for the point!
This make sense. I checked the user guide document page 59/60, where is written:
"When autozero is enabled (default), the multimeter internally disconnects the input signal following each measurement, and takes a zero reading. It then subtracts the zero reading from the preceding reading. This prevents offset voltages present on the multimeter’s input circuitry from affecting measurement accuracy."
The AutoZero is always ON when using the "Front-Panel Operation".
I'm going to use the ZERO:AUTO OFF SCPI command to see if this can help to speed-up the measurement in trade off of accuracy.
In the Keysight site
https://community.keysight.com/community/keysight-blogs/general-electronics-measurement/blog/2017/04/07/increasing-dmm-measurement-throughput, I found the following info :
"Therefore, if your measurements are taken in an environment with a stable temperature, or if there are several measurements taken in a short period of time (temperature changes occur over longer periods of time), the improvements in throughput by turning auto zero off will far outweigh any slight compromise in accuracy. For example, with auto zero off in a stable environment, the Keysight 34460A/61A/65A/70A DMMs typically adds only an additional 0.0002% of range +5 ?V for DCV or +5 m? for resistance accuracy specification"