NTPsec

crane3.services.mbix.ca

Report generated: Wed Jul 1 16:45:02 2026 UTC
Start Time: Wed Jun 24 16:45:01 2026 UTC
End Time: Wed Jul 1 16:45:01 2026 UTC
Report Period: 7.0 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 -51.536 -23.087 -17.500 -3.230 27.857 39.003 69.661 45.357 62.090 13.819 -0.000 µs -3.065 6.948
Local Clock Frequency Offset 78.412 78.443 78.480 78.661 78.740 78.767 78.807 0.260 0.323 0.080 78.639 ppm 9.435e+08 9.254e+11

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 5.428 9.171 11.189 18.035 26.353 30.229 42.846 15.164 21.058 4.643 18.322 µs 34.81 135.2

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 2.255 3.465 4.193 6.505 9.146 10.475 16.872 4.953 7.010 1.531 6.572 ppb 46 191.5

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 -51.536 -23.087 -17.500 -3.230 27.857 39.003 69.661 45.357 62.090 13.819 -0.000 µs -3.065 6.948

The clock offsets of the local clock as a histogram.

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



Local Temperatures

local temps plot

Local temperatures. These will be site-specific depending upon what temperature sensors you collect data from. Temperature changes affect the local clock crystal frequency and stability. The math of how temperature changes frequency is complex, and also depends on crystal aging. So there is no easy way to correct for it in software. This is the single most important component of frequency drift.

The Local Temperatures are from field 3 from the tempstats log file.



Local Frequency/Temp

local freq temps plot

Percentiles...... Ranges...... Skew- Kurt-
Name Min1%5%50%95% 99%Max   90%98%StdDev  MeanUnits nessosis
Local Clock Frequency Offset 78.412 78.443 78.480 78.661 78.740 78.767 78.807 0.260 0.323 0.080 78.639 ppm 9.435e+08 9.254e+11
Temp LM0 36.000 37.000 38.000 39.000 41.000 41.000 42.000 3.000 4.000 0.916 39.442 °C
Temp LM1 34.000 34.000 35.000 36.000 38.000 39.000 39.000 3.000 5.000 1.075 36.444 °C
Temp LM10 32.000 32.000 33.000 34.000 36.000 37.000 38.000 3.000 5.000 1.044 34.394 °C
Temp LM2 32.000 33.000 33.000 35.000 36.000 37.000 38.000 3.000 4.000 0.939 34.617 °C
Temp LM3 37.000 37.000 38.000 39.000 41.000 41.000 42.000 3.000 4.000 0.914 39.442 °C
Temp LM4 34.000 35.000 35.000 36.000 38.000 38.000 39.000 3.000 3.000 0.841 36.119 °C
Temp LM5 62.000 62.000 62.000 63.000 64.000 64.000 64.000 2.000 2.000 0.622 63.254 °C
Temp LM6 39.000 40.000 40.000 41.000 43.000 43.000 45.000 3.000 3.000 0.958 41.441 °C
Temp LM7 37.000 38.000 38.000 40.000 42.000 42.000 43.000 4.000 4.000 1.050 40.119 °C
Temp LM8 37.000 38.000 39.000 41.000 43.000 43.000 45.000 4.000 5.000 1.083 40.917 °C
Temp LM9 36.000 37.000 38.000 39.000 41.000 42.000 44.000 3.000 5.000 1.076 39.242 °C
Temp ZONE0 39.000 40.000 40.000 42.000 43.000 44.000 44.000 3.000 4.000 1.042 41.576 °C
Temp ZONE1 37.000 37.000 38.000 40.000 41.000 42.000 43.000 3.000 5.000 0.998 39.549 °C

The frequency offsets and temperatures. Showing frequency offset (red, in parts per million, scale on right) and the temperatures.

These are field 4 (frequency) from the loopstats log file, and field 3 from the tempstats 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 132.246.11.227

peer offset 132.246.11.227 plot

Percentiles...... Ranges...... Skew- Kurt-
Name Min1%5%50%95% 99%Max   90%98%StdDev  MeanUnits nessosis
Server Offset 132.246.11.227 1.555 1.849 1.923 2.103 2.195 17.934 18.080 0.272 16.085 2.368 2.453 ms 6.487 42.68

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 142.3.100.2

peer offset 142.3.100.2 plot

Percentiles...... Ranges...... Skew- Kurt-
Name Min1%5%50%95% 99%Max   90%98%StdDev  MeanUnits nessosis
Server Offset 142.3.100.2 -2,543.593 -49.548 -34.456 3.692 45.911 69.029 87.658 80.367 118.577 62.808 2.706 µs -37.05 1480

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::199 (ntp2.wiktel.com)

peer offset 2600:2600::199 plot

Percentiles...... Ranges...... Skew- Kurt-
Name Min1%5%50%95% 99%Max   90%98%StdDev  MeanUnits nessosis
Server Offset 2600:2600::199 (ntp2.wiktel.com) -2,772.580 30.583 52.792 366.399 400.700 412.260 428.734 347.908 381.677 112.673 342.137 µs 2.954 233

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:fde5:2a::13

peer offset 2602:fde5:2a::13 plot

Percentiles...... Ranges...... Skew- Kurt-
Name Min1%5%50%95% 99%Max   90%98%StdDev  MeanUnits nessosis
Server Offset 2602:fde5:2a::13 1.425 1.450 1.459 1.492 2.072 2.086 2.102 0.612 0.637 0.262 1.653 ms 167.1 988.7

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::1 (time.cloudflare.com)

peer offset 2606:4700:f1::1 plot

Percentiles...... Ranges...... Skew- Kurt-
Name Min1%5%50%95% 99%Max   90%98%StdDev  MeanUnits nessosis
Server Offset 2606:4700:f1::1 (time.cloudflare.com) -2.042 -1.643 -1.514 -1.172 -0.987 -0.836 -0.370 0.527 0.807 0.154 -1.192 ms -701.1 6403

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::123:1 (ntp1.doit.wisc.edu)

peer offset 2607:f388::123:1 plot

Percentiles...... Ranges...... Skew- Kurt-
Name Min1%5%50%95% 99%Max   90%98%StdDev  MeanUnits nessosis
Server Offset 2607:f388::123:1 (ntp1.doit.wisc.edu) -0.589 -0.540 -0.515 -0.452 2.646 5.173 11.829 3.160 5.713 1.241 0.090 ms -0.5217 9.606

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 PPS(0)

peer offset PPS(0) plot

Percentiles...... Ranges...... Skew- Kurt-
Name Min1%5%50%95% 99%Max   90%98%StdDev  MeanUnits nessosis
Server Offset PPS(0) -51.537 -23.088 -17.501 -3.231 27.858 39.004 69.662 45.359 62.092 13.820 -0.001 µs -3.065 6.948

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 132.246.11.227

peer jitter 132.246.11.227 plot

Percentiles...... Ranges...... Skew- Kurt-
Name Min1%5%50%95% 99%Max   90%98%StdDev  MeanUnits nessosis
Server Jitter 132.246.11.227 0.024 0.042 0.064 0.271 1.369 4.633 80.072 1.305 4.590 2.751 0.570 ms 20.91 595.8

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 142.3.100.2

peer jitter 142.3.100.2 plot

Percentiles...... Ranges...... Skew- Kurt-
Name Min1%5%50%95% 99%Max   90%98%StdDev  MeanUnits nessosis
Server Jitter 142.3.100.2 0.000 0.016 0.022 0.040 0.099 0.559 182.803 0.077 0.543 8.191 0.562 ms 15.23 324.1

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::199 (ntp2.wiktel.com)

peer jitter 2600:2600::199 plot

Percentiles...... Ranges...... Skew- Kurt-
Name Min1%5%50%95% 99%Max   90%98%StdDev  MeanUnits nessosis
Server Jitter 2600:2600::199 (ntp2.wiktel.com) 4.958 8.256 10.178 19.715 42.329 66.818 4,226.274 32.151 58.562 151.455 29.570 µs 21.14 551.7

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:fde5:2a::13

peer jitter 2602:fde5:2a::13 plot

Percentiles...... Ranges...... Skew- Kurt-
Name Min1%5%50%95% 99%Max   90%98%StdDev  MeanUnits nessosis
Server Jitter 2602:fde5:2a::13 0.004 0.008 0.011 0.041 0.578 0.593 5.015 0.567 0.585 0.293 0.243 ms 5.174 85.35

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::1 (time.cloudflare.com)

peer jitter 2606:4700:f1::1 plot

Percentiles...... Ranges...... Skew- Kurt-
Name Min1%5%50%95% 99%Max   90%98%StdDev  MeanUnits nessosis
Server Jitter 2606:4700:f1::1 (time.cloudflare.com) 5.317 12.580 17.391 44.138 116.428 356.615 791.196 99.037 344.035 59.950 56.788 µs 5.66 46.81

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::123:1 (ntp1.doit.wisc.edu)

peer jitter 2607:f388::123:1 plot

Percentiles...... Ranges...... Skew- Kurt-
Name Min1%5%50%95% 99%Max   90%98%StdDev  MeanUnits nessosis
Server Jitter 2607:f388::123:1 (ntp1.doit.wisc.edu) 0.006 0.010 0.014 0.034 19.096 26.817 54.082 19.081 26.807 7.360 4.272 ms 0.3758 4.144

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 PPS(0)

peer jitter PPS(0) plot

Percentiles...... Ranges...... Skew- Kurt-
Name Min1%5%50%95% 99%Max   90%98%StdDev  MeanUnits nessosis
Server Jitter PPS(0) 1.695 5.081 7.414 16.926 34.066 43.634 73.377 26.652 38.553 8.261 18.292 µs 6.48 20.76

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 78.412 78.443 78.480 78.661 78.740 78.767 78.807 0.260 0.323 0.080 78.639 ppm 9.435e+08 9.254e+11
Local Clock Time Offset -51.536 -23.087 -17.500 -3.230 27.857 39.003 69.661 45.357 62.090 13.819 -0.000 µs -3.065 6.948
Local RMS Frequency Jitter 2.255 3.465 4.193 6.505 9.146 10.475 16.872 4.953 7.010 1.531 6.572 ppb 46 191.5
Local RMS Time Jitter 5.428 9.171 11.189 18.035 26.353 30.229 42.846 15.164 21.058 4.643 18.322 µs 34.81 135.2
Server Jitter 132.246.11.227 0.024 0.042 0.064 0.271 1.369 4.633 80.072 1.305 4.590 2.751 0.570 ms 20.91 595.8
Server Jitter 142.3.100.2 0.000 0.016 0.022 0.040 0.099 0.559 182.803 0.077 0.543 8.191 0.562 ms 15.23 324.1
Server Jitter 2600:2600::199 (ntp2.wiktel.com) 4.958 8.256 10.178 19.715 42.329 66.818 4,226.274 32.151 58.562 151.455 29.570 µs 21.14 551.7
Server Jitter 2602:fde5:2a::13 0.004 0.008 0.011 0.041 0.578 0.593 5.015 0.567 0.585 0.293 0.243 ms 5.174 85.35
Server Jitter 2606:4700:f1::1 (time.cloudflare.com) 5.317 12.580 17.391 44.138 116.428 356.615 791.196 99.037 344.035 59.950 56.788 µs 5.66 46.81
Server Jitter 2607:f388::123:1 (ntp1.doit.wisc.edu) 0.006 0.010 0.014 0.034 19.096 26.817 54.082 19.081 26.807 7.360 4.272 ms 0.3758 4.144
Server Jitter PPS(0) 1.695 5.081 7.414 16.926 34.066 43.634 73.377 26.652 38.553 8.261 18.292 µs 6.48 20.76
Server Offset 132.246.11.227 1.555 1.849 1.923 2.103 2.195 17.934 18.080 0.272 16.085 2.368 2.453 ms 6.487 42.68
Server Offset 142.3.100.2 -2,543.593 -49.548 -34.456 3.692 45.911 69.029 87.658 80.367 118.577 62.808 2.706 µs -37.05 1480
Server Offset 2600:2600::199 (ntp2.wiktel.com) -2,772.580 30.583 52.792 366.399 400.700 412.260 428.734 347.908 381.677 112.673 342.137 µs 2.954 233
Server Offset 2602:fde5:2a::13 1.425 1.450 1.459 1.492 2.072 2.086 2.102 0.612 0.637 0.262 1.653 ms 167.1 988.7
Server Offset 2606:4700:f1::1 (time.cloudflare.com) -2.042 -1.643 -1.514 -1.172 -0.987 -0.836 -0.370 0.527 0.807 0.154 -1.192 ms -701.1 6403
Server Offset 2607:f388::123:1 (ntp1.doit.wisc.edu) -0.589 -0.540 -0.515 -0.452 2.646 5.173 11.829 3.160 5.713 1.241 0.090 ms -0.5217 9.606
Server Offset PPS(0) -51.537 -23.088 -17.501 -3.231 27.858 39.004 69.662 45.359 62.092 13.820 -0.001 µs -3.065 6.948
Temp LM0 36.000 37.000 38.000 39.000 41.000 41.000 42.000 3.000 4.000 0.916 39.442 °C
Temp LM1 34.000 34.000 35.000 36.000 38.000 39.000 39.000 3.000 5.000 1.075 36.444 °C
Temp LM10 32.000 32.000 33.000 34.000 36.000 37.000 38.000 3.000 5.000 1.044 34.394 °C
Temp LM2 32.000 33.000 33.000 35.000 36.000 37.000 38.000 3.000 4.000 0.939 34.617 °C
Temp LM3 37.000 37.000 38.000 39.000 41.000 41.000 42.000 3.000 4.000 0.914 39.442 °C
Temp LM4 34.000 35.000 35.000 36.000 38.000 38.000 39.000 3.000 3.000 0.841 36.119 °C
Temp LM5 62.000 62.000 62.000 63.000 64.000 64.000 64.000 2.000 2.000 0.622 63.254 °C
Temp LM6 39.000 40.000 40.000 41.000 43.000 43.000 45.000 3.000 3.000 0.958 41.441 °C
Temp LM7 37.000 38.000 38.000 40.000 42.000 42.000 43.000 4.000 4.000 1.050 40.119 °C
Temp LM8 37.000 38.000 39.000 41.000 43.000 43.000 45.000 4.000 5.000 1.083 40.917 °C
Temp LM9 36.000 37.000 38.000 39.000 41.000 42.000 44.000 3.000 5.000 1.076 39.242 °C
Temp ZONE0 39.000 40.000 40.000 42.000 43.000 44.000 44.000 3.000 4.000 1.042 41.576 °C
Temp ZONE1 37.000 37.000 38.000 40.000 41.000 42.000 43.000 3.000 5.000 0.998 39.549 °C
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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