NTPsec

ntp2.wiktel.com

Report generated: Wed Jul 1 17:53:01 2026 UTC
Start Time: Tue Jun 30 17:53:00 2026 UTC
End Time: Wed Jul 1 17:53:00 2026 UTC
Report Period: 1.0 days

Top   Daily Stats   Weekly Stats  

Local Clock Time/Frequency Offsets

local offset plot

Percentiles...... Ranges...... Skew- Kurt-
Name Min1%5%50%95% 99%Max   90%98%StdDev  MeanUnits nessosis
Local Clock Time Offset -23.605 -10.020 -6.276 0.647 3.428 4.792 9.603 9.704 14.812 2.946 -0.006 µs -5.651 20.55
Local Clock Frequency Offset -13.810 -13.748 -13.723 -13.587 -13.184 -13.043 -12.979 0.539 0.704 0.163 -13.553 ppm -6.007e+05 5.07e+07

The time and frequency offsets between the ntpd calculated time and the local system clock. Showing frequency offset (red, in parts per million, scale on right) and the time offset (blue, in μs, scale on left). Quick changes in time offset will lead to larger frequency offsets.

These are fields 3 (time) and 4 (frequency) from the loopstats log file.



Local RMS Time Jitter

local jitter plot

Percentiles...... Ranges...... Skew- Kurt-
Name Min1%5%50%95% 99%Max   90%98%StdDev  MeanUnits nessosis
Local RMS Time Jitter 0.755 1.327 1.824 3.627 6.148 7.626 11.246 4.324 6.299 1.335 3.763 µs 12.16 39.65

The RMS Jitter of the local clock offset. In other words, how fast the local clock offset is changing.

Lower is better. An ideal system would be a horizontal line at 0μs.

RMS jitter is field 5 in the loopstats log file.



Local RMS Frequency Jitter

local stability plot

Percentiles...... Ranges...... Skew- Kurt-
Name Min1%5%50%95% 99%Max   90%98%StdDev  MeanUnits nessosis
Local RMS Frequency Jitter 1.223 1.990 2.683 5.281 8.791 10.704 16.590 6.108 8.714 1.867 5.444 ppb 13.41 44

The RMS Frequency Jitter (aka wander) of the local clock's frequency. In other words, how fast the local clock changes frequency.

Lower is better. An ideal clock would be a horizontal line at 0ppm.

RMS Frequency Jitter is field 6 in the loopstats log file.



Local Clock Time Offset Histogram

local offset histogram plot

Percentiles...... Ranges...... Skew- Kurt-
Name Min1%5%50%95% 99%Max   90%98%StdDev  MeanUnits nessosis
Local Clock Offset -23.605 -10.020 -6.276 0.647 3.428 4.792 9.603 9.704 14.812 2.946 -0.006 µs -5.651 20.55

The clock offsets of the local clock as a histogram.

The Local Clock Offset is field 3 from the loopstats log file.



Server Offsets

peer offsets plot

The offset of all refclocks and servers. This can be useful to see if offset changes are happening in a single clock or all clocks together.

Clock Offset is field 5 in the peerstats log file.



Server Offset 132.163.97.5

peer offset 132.163.97.5 plot

Percentiles...... Ranges...... Skew- Kurt-
Name Min1%5%50%95% 99%Max   90%98%StdDev  MeanUnits nessosis
Server Offset 132.163.97.5 -1.418 -1.406 -1.389 -1.033 -0.958 -0.403 -0.363 0.431 1.003 0.190 -1.050 ms -295.6 2042

The offset of a server in seconds. This is useful to see how the measured offset is behaving.

The chart also plots offset±rtt, where rtt is the round trip time to the server. NTP can not really know the offset of a remote chimer, NTP computes it by subtracting rtt/2 from the offset. Plotting the offset±rtt reverses this calculation to more easily see the effects of rtt changes.

Closer to 0s is better. An ideal system would be a horizontal line at 0s. Typical 90% ranges may be: local LAN server 80µs; 90% ranges for WAN server may be 4ms and much larger.

Clock Offset is field 5 in the peerstats log file. The Round Trip Time (rtt) is field 6 in the peerstats log file.



Server Offset 132.246.11.238

peer offset 132.246.11.238 plot

Percentiles...... Ranges...... Skew- Kurt-
Name Min1%5%50%95% 99%Max   90%98%StdDev  MeanUnits nessosis
Server Offset 132.246.11.238 -727.264 -658.069 382.260 715.096 912.796 962.567 1,116.854 530.536 1,620.636 309.843 609.464 µs 1.363 7.67

The offset of a server in seconds. This is useful to see how the measured offset is behaving.

The chart also plots offset±rtt, where rtt is the round trip time to the server. NTP can not really know the offset of a remote chimer, NTP computes it by subtracting rtt/2 from the offset. Plotting the offset±rtt reverses this calculation to more easily see the effects of rtt changes.

Closer to 0s is better. An ideal system would be a horizontal line at 0s. Typical 90% ranges may be: local LAN server 80µs; 90% ranges for WAN server may be 4ms and much larger.

Clock Offset is field 5 in the peerstats log file. The Round Trip Time (rtt) is field 6 in the peerstats log file.



Server Offset 134.84.84.84

peer offset 134.84.84.84 plot

Percentiles...... Ranges...... Skew- Kurt-
Name Min1%5%50%95% 99%Max   90%98%StdDev  MeanUnits nessosis
Server Offset 134.84.84.84 -71.780 -66.326 -40.315 19.665 62.665 81.932 93.830 102.980 148.258 31.078 17.071 µs -1.815 4.966

The offset of a server in seconds. This is useful to see how the measured offset is behaving.

The chart also plots offset±rtt, where rtt is the round trip time to the server. NTP can not really know the offset of a remote chimer, NTP computes it by subtracting rtt/2 from the offset. Plotting the offset±rtt reverses this calculation to more easily see the effects of rtt changes.

Closer to 0s is better. An ideal system would be a horizontal line at 0s. Typical 90% ranges may be: local LAN server 80µs; 90% ranges for WAN server may be 4ms and much larger.

Clock Offset is field 5 in the peerstats log file. The Round Trip Time (rtt) is field 6 in the peerstats log file.



Server Offset 204.9.54.119

peer offset 204.9.54.119 plot

Percentiles...... Ranges...... Skew- Kurt-
Name Min1%5%50%95% 99%Max   90%98%StdDev  MeanUnits nessosis
Server Offset 204.9.54.119 -1.035 -1.032 -1.029 -1.023 -1.014 -1.011 -1.007 0.015 0.020 0.005 -1.022 ms -1.17e+07 2.656e+09

The offset of a server in seconds. This is useful to see how the measured offset is behaving.

The chart also plots offset±rtt, where rtt is the round trip time to the server. NTP can not really know the offset of a remote chimer, NTP computes it by subtracting rtt/2 from the offset. Plotting the offset±rtt reverses this calculation to more easily see the effects of rtt changes.

Closer to 0s is better. An ideal system would be a horizontal line at 0s. Typical 90% ranges may be: local LAN server 80µs; 90% ranges for WAN server may be 4ms and much larger.

Clock Offset is field 5 in the peerstats log file. The Round Trip Time (rtt) is field 6 in the peerstats log file.



Server Offset 2600:2600::99 (ntp1.wiktel.com)

peer offset 2600:2600::99 plot

Percentiles...... Ranges...... Skew- Kurt-
Name Min1%5%50%95% 99%Max   90%98%StdDev  MeanUnits nessosis
Server Offset 2600:2600::99 (ntp1.wiktel.com) -369.537 -367.615 -360.091 -344.154 -328.140 -321.101 -320.147 31.951 46.514 9.559 -344.425 µs -5.089e+04 1.889e+06

The offset of a server in seconds. This is useful to see how the measured offset is behaving.

The chart also plots offset±rtt, where rtt is the round trip time to the server. NTP can not really know the offset of a remote chimer, NTP computes it by subtracting rtt/2 from the offset. Plotting the offset±rtt reverses this calculation to more easily see the effects of rtt changes.

Closer to 0s is better. An ideal system would be a horizontal line at 0s. Typical 90% ranges may be: local LAN server 80µs; 90% ranges for WAN server may be 4ms and much larger.

Clock Offset is field 5 in the peerstats log file. The Round Trip Time (rtt) is field 6 in the peerstats log file.



Server Offset 2602:fd53:11e:123::1 (time1.mbix.ca)

peer offset 2602:fd53:11e:123::1 plot

Percentiles...... Ranges...... Skew- Kurt-
Name Min1%5%50%95% 99%Max   90%98%StdDev  MeanUnits nessosis
Server Offset 2602:fd53:11e:123::1 (time1.mbix.ca) -420.434 -413.896 -400.635 -371.345 -322.000 -40.269 2,750.330 78.635 373.627 193.483 -348.561 µs -16.13 175.2

The offset of a server in seconds. This is useful to see how the measured offset is behaving.

The chart also plots offset±rtt, where rtt is the round trip time to the server. NTP can not really know the offset of a remote chimer, NTP computes it by subtracting rtt/2 from the offset. Plotting the offset±rtt reverses this calculation to more easily see the effects of rtt changes.

Closer to 0s is better. An ideal system would be a horizontal line at 0s. Typical 90% ranges may be: local LAN server 80µs; 90% ranges for WAN server may be 4ms and much larger.

Clock Offset is field 5 in the peerstats log file. The Round Trip Time (rtt) is field 6 in the peerstats log file.



Server Offset 2606:4700:f1::123 (time.cloudflare.com)

peer offset 2606:4700:f1::123 plot

Percentiles...... Ranges...... Skew- Kurt-
Name Min1%5%50%95% 99%Max   90%98%StdDev  MeanUnits nessosis
Server Offset 2606:4700:f1::123 (time.cloudflare.com) -484.831 -273.536 -182.385 -15.315 132.343 202.967 367.629 314.728 476.503 100.370 -22.046 µs -5.884 18.27

The offset of a server in seconds. This is useful to see how the measured offset is behaving.

The chart also plots offset±rtt, where rtt is the round trip time to the server. NTP can not really know the offset of a remote chimer, NTP computes it by subtracting rtt/2 from the offset. Plotting the offset±rtt reverses this calculation to more easily see the effects of rtt changes.

Closer to 0s is better. An ideal system would be a horizontal line at 0s. Typical 90% ranges may be: local LAN server 80µs; 90% ranges for WAN server may be 4ms and much larger.

Clock Offset is field 5 in the peerstats log file. The Round Trip Time (rtt) is field 6 in the peerstats log file.



Server Offset 2607:f388::123:2 (ntp2.doit.wisc.edu)

peer offset 2607:f388::123:2 plot

Percentiles...... Ranges...... Skew- Kurt-
Name Min1%5%50%95% 99%Max   90%98%StdDev  MeanUnits nessosis
Server Offset 2607:f388::123:2 (ntp2.doit.wisc.edu) -107.654 -93.201 -72.162 -18.840 51.667 88.476 94.001 123.829 181.677 36.246 -16.448 µs -6.956 17.88

The offset of a server in seconds. This is useful to see how the measured offset is behaving.

The chart also plots offset±rtt, where rtt is the round trip time to the server. NTP can not really know the offset of a remote chimer, NTP computes it by subtracting rtt/2 from the offset. Plotting the offset±rtt reverses this calculation to more easily see the effects of rtt changes.

Closer to 0s is better. An ideal system would be a horizontal line at 0s. Typical 90% ranges may be: local LAN server 80µs; 90% ranges for WAN server may be 4ms and much larger.

Clock Offset is field 5 in the peerstats log file. The Round Trip Time (rtt) is field 6 in the peerstats log file.



Server Offset SHM(1)

peer offset SHM(1) plot

Percentiles...... Ranges...... Skew- Kurt-
Name Min1%5%50%95% 99%Max   90%98%StdDev  MeanUnits nessosis
Server Offset SHM(1) -23.606 -10.021 -6.277 0.648 3.429 4.793 9.604 9.706 14.814 2.947 -0.005 µs -5.65 20.54

The offset of a server in seconds. This is useful to see how the measured offset is behaving.

The chart also plots offset±rtt, where rtt is the round trip time to the server. NTP can not really know the offset of a remote chimer, NTP computes it by subtracting rtt/2 from the offset. Plotting the offset±rtt reverses this calculation to more easily see the effects of rtt changes.

Closer to 0s is better. An ideal system would be a horizontal line at 0s. Typical 90% ranges may be: local LAN server 80µs; 90% ranges for WAN server may be 4ms and much larger.

Clock Offset is field 5 in the peerstats log file. The Round Trip Time (rtt) is field 6 in the peerstats log file.



Server Jitters

peer jitters plot

The RMS Jitter of all refclocks and servers. Jitter is the current estimated dispersion, in other words the variation in offset between samples.

Closer to 0s is better. An ideal system would be a horizontal line at 0s.

RMS Jitter is field 8 in the peerstats log file.



Server Jitter 132.163.97.5

peer jitter 132.163.97.5 plot

Percentiles...... Ranges...... Skew- Kurt-
Name Min1%5%50%95% 99%Max   90%98%StdDev  MeanUnits nessosis
Server Jitter 132.163.97.5 14.218 15.511 19.622 49.537 359.200 384.375 672.628 339.578 368.864 132.506 134.385 µs 0.8738 2.408

The RMS Jitter of a server. Jitter is the current estimated dispersion, in other words the variation in offset between samples.

Closer to 0s is better. An ideal system would be a horizontal line at 0s.

RMS Jitter is field 8 in the peerstats log file.



Server Jitter 132.246.11.238

peer jitter 132.246.11.238 plot

Percentiles...... Ranges...... Skew- Kurt-
Name Min1%5%50%95% 99%Max   90%98%StdDev  MeanUnits nessosis
Server Jitter 132.246.11.238 0.041 0.063 0.107 0.370 1.866 3.453 16.159 1.759 3.390 1.536 0.630 ms 7.03 70.88

The RMS Jitter of a server. Jitter is the current estimated dispersion, in other words the variation in offset between samples.

Closer to 0s is better. An ideal system would be a horizontal line at 0s.

RMS Jitter is field 8 in the peerstats log file.



Server Jitter 134.84.84.84

peer jitter 134.84.84.84 plot

Percentiles...... Ranges...... Skew- Kurt-
Name Min1%5%50%95% 99%Max   90%98%StdDev  MeanUnits nessosis
Server Jitter 134.84.84.84 2.827 3.516 4.836 14.082 36.766 52.869 118.362 31.930 49.353 12.126 17.201 µs 4.111 25.33

The RMS Jitter of a server. Jitter is the current estimated dispersion, in other words the variation in offset between samples.

Closer to 0s is better. An ideal system would be a horizontal line at 0s.

RMS Jitter is field 8 in the peerstats log file.



Server Jitter 204.9.54.119

peer jitter 204.9.54.119 plot

Percentiles...... Ranges...... Skew- Kurt-
Name Min1%5%50%95% 99%Max   90%98%StdDev  MeanUnits nessosis
Server Jitter 204.9.54.119 1.770 2.775 5.073 9.423 16.190 20.398 51.296 11.117 17.623 4.724 9.995 µs 9.139 66.22

The RMS Jitter of a server. Jitter is the current estimated dispersion, in other words the variation in offset between samples.

Closer to 0s is better. An ideal system would be a horizontal line at 0s.

RMS Jitter is field 8 in the peerstats log file.



Server Jitter 2600:2600::99 (ntp1.wiktel.com)

peer jitter 2600:2600::99 plot

Percentiles...... Ranges...... Skew- Kurt-
Name Min1%5%50%95% 99%Max   90%98%StdDev  MeanUnits nessosis
Server Jitter 2600:2600::99 (ntp1.wiktel.com) 5.258 7.566 9.646 19.852 34.142 37.793 40.878 24.496 30.227 7.435 20.485 µs 11.13 33.8

The RMS Jitter of a server. Jitter is the current estimated dispersion, in other words the variation in offset between samples.

Closer to 0s is better. An ideal system would be a horizontal line at 0s.

RMS Jitter is field 8 in the peerstats log file.



Server Jitter 2602:fd53:11e:123::1 (time1.mbix.ca)

peer jitter 2602:fd53:11e:123::1 plot

Percentiles...... Ranges...... Skew- Kurt-
Name Min1%5%50%95% 99%Max   90%98%StdDev  MeanUnits nessosis
Server Jitter 2602:fd53:11e:123::1 (time1.mbix.ca) 0.006 0.007 0.010 0.021 0.045 1.209 2.793 0.035 1.201 0.189 0.041 ms 9.337 129.3

The RMS Jitter of a server. Jitter is the current estimated dispersion, in other words the variation in offset between samples.

Closer to 0s is better. An ideal system would be a horizontal line at 0s.

RMS Jitter is field 8 in the peerstats log file.



Server Jitter 2606:4700:f1::123 (time.cloudflare.com)

peer jitter 2606:4700:f1::123 plot

Percentiles...... Ranges...... Skew- Kurt-
Name Min1%5%50%95% 99%Max   90%98%StdDev  MeanUnits nessosis
Server Jitter 2606:4700:f1::123 (time.cloudflare.com) 9.948 12.839 17.247 54.446 212.942 250.921 271.114 195.695 238.082 61.079 77.666 µs 2.111 5.639

The RMS Jitter of a server. Jitter is the current estimated dispersion, in other words the variation in offset between samples.

Closer to 0s is better. An ideal system would be a horizontal line at 0s.

RMS Jitter is field 8 in the peerstats log file.



Server Jitter 2607:f388::123:2 (ntp2.doit.wisc.edu)

peer jitter 2607:f388::123:2 plot

Percentiles...... Ranges...... Skew- Kurt-
Name Min1%5%50%95% 99%Max   90%98%StdDev  MeanUnits nessosis
Server Jitter 2607:f388::123:2 (ntp2.doit.wisc.edu) 6.415 8.224 11.473 22.181 40.443 55.100 56.233 28.970 46.876 8.964 23.717 µs 10.27 33.34

The RMS Jitter of a server. Jitter is the current estimated dispersion, in other words the variation in offset between samples.

Closer to 0s is better. An ideal system would be a horizontal line at 0s.

RMS Jitter is field 8 in the peerstats log file.



Server Jitter SHM(1)

peer jitter SHM(1) plot

Percentiles...... Ranges...... Skew- Kurt-
Name Min1%5%50%95% 99%Max   90%98%StdDev  MeanUnits nessosis
Server Jitter SHM(1) 0.227 0.581 0.947 3.229 7.831 10.851 24.027 6.884 10.270 2.229 3.652 µs 3.597 12.84

The RMS Jitter of a server. Jitter is the current estimated dispersion, in other words the variation in offset between samples.

Closer to 0s is better. An ideal system would be a horizontal line at 0s.

RMS Jitter is field 8 in the peerstats log file.



Summary


Percentiles...... Ranges...... Skew- Kurt-
Name Min1%5%50%95% 99%Max   90%98%StdDev  MeanUnits nessosis
Local Clock Frequency Offset -13.810 -13.748 -13.723 -13.587 -13.184 -13.043 -12.979 0.539 0.704 0.163 -13.553 ppm -6.007e+05 5.07e+07
Local Clock Time Offset -23.605 -10.020 -6.276 0.647 3.428 4.792 9.603 9.704 14.812 2.946 -0.006 µs -5.651 20.55
Local RMS Frequency Jitter 1.223 1.990 2.683 5.281 8.791 10.704 16.590 6.108 8.714 1.867 5.444 ppb 13.41 44
Local RMS Time Jitter 0.755 1.327 1.824 3.627 6.148 7.626 11.246 4.324 6.299 1.335 3.763 µs 12.16 39.65
Server Jitter 132.163.97.5 14.218 15.511 19.622 49.537 359.200 384.375 672.628 339.578 368.864 132.506 134.385 µs 0.8738 2.408
Server Jitter 132.246.11.238 0.041 0.063 0.107 0.370 1.866 3.453 16.159 1.759 3.390 1.536 0.630 ms 7.03 70.88
Server Jitter 134.84.84.84 2.827 3.516 4.836 14.082 36.766 52.869 118.362 31.930 49.353 12.126 17.201 µs 4.111 25.33
Server Jitter 204.9.54.119 1.770 2.775 5.073 9.423 16.190 20.398 51.296 11.117 17.623 4.724 9.995 µs 9.139 66.22
Server Jitter 2600:2600::99 (ntp1.wiktel.com) 5.258 7.566 9.646 19.852 34.142 37.793 40.878 24.496 30.227 7.435 20.485 µs 11.13 33.8
Server Jitter 2602:fd53:11e:123::1 (time1.mbix.ca) 0.006 0.007 0.010 0.021 0.045 1.209 2.793 0.035 1.201 0.189 0.041 ms 9.337 129.3
Server Jitter 2606:4700:f1::123 (time.cloudflare.com) 9.948 12.839 17.247 54.446 212.942 250.921 271.114 195.695 238.082 61.079 77.666 µs 2.111 5.639
Server Jitter 2607:f388::123:2 (ntp2.doit.wisc.edu) 6.415 8.224 11.473 22.181 40.443 55.100 56.233 28.970 46.876 8.964 23.717 µs 10.27 33.34
Server Jitter SHM(1) 0.227 0.581 0.947 3.229 7.831 10.851 24.027 6.884 10.270 2.229 3.652 µs 3.597 12.84
Server Offset 132.163.97.5 -1.418 -1.406 -1.389 -1.033 -0.958 -0.403 -0.363 0.431 1.003 0.190 -1.050 ms -295.6 2042
Server Offset 132.246.11.238 -727.264 -658.069 382.260 715.096 912.796 962.567 1,116.854 530.536 1,620.636 309.843 609.464 µs 1.363 7.67
Server Offset 134.84.84.84 -71.780 -66.326 -40.315 19.665 62.665 81.932 93.830 102.980 148.258 31.078 17.071 µs -1.815 4.966
Server Offset 204.9.54.119 -1.035 -1.032 -1.029 -1.023 -1.014 -1.011 -1.007 0.015 0.020 0.005 -1.022 ms -1.17e+07 2.656e+09
Server Offset 2600:2600::99 (ntp1.wiktel.com) -369.537 -367.615 -360.091 -344.154 -328.140 -321.101 -320.147 31.951 46.514 9.559 -344.425 µs -5.089e+04 1.889e+06
Server Offset 2602:fd53:11e:123::1 (time1.mbix.ca) -420.434 -413.896 -400.635 -371.345 -322.000 -40.269 2,750.330 78.635 373.627 193.483 -348.561 µs -16.13 175.2
Server Offset 2606:4700:f1::123 (time.cloudflare.com) -484.831 -273.536 -182.385 -15.315 132.343 202.967 367.629 314.728 476.503 100.370 -22.046 µs -5.884 18.27
Server Offset 2607:f388::123:2 (ntp2.doit.wisc.edu) -107.654 -93.201 -72.162 -18.840 51.667 88.476 94.001 123.829 181.677 36.246 -16.448 µs -6.956 17.88
Server Offset SHM(1) -23.606 -10.021 -6.277 0.648 3.429 4.793 9.604 9.706 14.814 2.947 -0.005 µs -5.65 20.54
Summary as CSV file


Glossary:

frequency offset:
The difference between the ntpd calculated frequency and the local system clock frequency (usually in parts per million, ppm)
jitter, dispersion:
The short term change in a value. NTP measures Local Time Jitter, Refclock Jitter, and Server Jitter in seconds. Local Frequency Jitter is in ppm or ppb.
kurtosis, Kurt:
The kurtosis of a random variable X is the fourth standardized moment and is a dimension-less ratio. ntpviz uses the Pearson's moment coefficient of kurtosis. A normal distribution has a kurtosis of three. NIST describes a kurtosis over three as "heavy tailed" and one under three as "light tailed".
ms, millisecond:
One thousandth of a second = 0.001 seconds, 1e-3 seconds
mu, mean:
The arithmetic mean: the sum of all the values divided by the number of values. The formula for mu is: "mu = (∑xi) / N". Where xi denotes the data points and N is the number of data points.
ns, nanosecond:
One billionth of a second, also one thousandth of a microsecond, 0.000000001 seconds and 1e-9 seconds.
percentile:
The value below which a given percentage of values fall.
ppb, parts per billion:
Ratio between two values. These following are all the same: 1 ppb, one in one billion, 1/1,000,000,000, 0.000,000,001, 1e-9 and 0.000,000,1%
ppm, parts per million:
Ratio between two values. These following are all the same: 1 ppm, one in one million, 1/1,000,000, 0.000,001, and 0.000,1%
‰, parts per thousand:
Ratio between two values. These following are all the same: 1 ‰. one in one thousand, 1/1,000, 0.001, and 0.1%
refclock:
Reference clock, a local GPS module or other local source of time.
remote clock:
Any clock reached over the network, LAN or WAN. Also called a peer or server.
time offset:
The difference between the ntpd calculated time and the local system clock's time. Also called phase offset.
σ, sigma:
Sigma denotes the standard deviation (SD) and is centered on the arithmetic mean of the data set. The SD is simply the square root of the variance of the data set. Two sigma is simply twice the standard deviation. Three sigma is three times sigma. Smaller is better.
The formula for sigma is: "σ = √[ ∑(xi-mu)^2 / N ]". Where xi denotes the data points and N is the number of data points.
skewness, Skew:
The skewness of a random variable X is the third standardized moment and is a dimension-less ratio. ntpviz uses the Pearson's moment coefficient of skewness. Wikipedia describes it best: "The qualitative interpretation of the skew is complicated and unintuitive."
A normal distribution has a skewness of zero.
upstream clock:
Any server or reference clock used as a source of time.
µs, us, microsecond:
One millionth of a second, also one thousandth of a millisecond, 0.000,001 seconds, and 1e-6 seconds.



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