Keysight Technologies 3458A Guide D'utilisation page 329

For sampled ACV or ACDCV, random sampling (SETACV RNDM) has a fixed
resolution of 4.5 digits that cannot be changed. For synchronous sampling
(SETACV SYNC), a %_resolution parameter of 0.001 = 7.5 digits; 0.01 = 6.5 digits;
0.1 = 5.5 digits; and 1= 4.5 digits.
For all other functions (except DSAC, DSDC, SSAC, and SSDC): %_resolution is
ignored for these functions), the multimeter multiplies %_resolution times the
present measurement range (1 V, 10 V, 100 V, etc.) to determine the resolution. To
compute the %_resolution parameter, use the equation:
%_resolution = (actual resolution/range) × 100.
For example, suppose you are measuring DC voltage on the 10 V range and you
want 100 µV of resolution. The equation evaluates to:
%_resolution = (.0001 /10) × 100 = .001
Power-on %_resolution none. At power-on, the resolution is determined by the
NPLC command which produces 8 ½ digits. (The power-on value for NDIG masks
1 display digit causing the multimeter to display only 7 ½ digits. You can use the
NDIG 8 command to display all 8 ½ digits.)
Default %_resolution:
Keysight 3458A User's Guide
%_resolution parameter
.00001
.0001
.001
.01
.1
For frequency or period measurements, the default %_resolution is .00001
which selects a gate time of 1 s and 7 digits of resolution.
For sampled ACV or ACDCV, the default %_resolution is 0.01% for SETACV
SYNC or 0.4% for SETACV RNDM.
For all other measurement functions, the default resolution is determined by
the present integration time.
Command Reference
Selects gate time
1 s
100 ms
10 ms
1 ms
100 µs
6
Digits of resolution
7
7
6
5
4
329