NTPsec

ntp1.wiktel.com

Report generated: Sat Sep 13 04:45:02 2025 UTC
Start Time: Sat Sep 6 04:45:00 2025 UTC
End Time: Sat Sep 13 04:45:00 2025 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 -10.434 -4.647 -3.537 -0.578 4.888 6.199 18.230 8.425 10.846 2.653 -0.001 µs -3.424 7.458
Local Clock Frequency Offset 17.251 17.322 17.385 17.495 17.587 17.610 17.634 0.203 0.287 0.062 17.493 ppm 2.258e+07 6.381e+09

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 0.300 0.444 0.522 0.772 1.378 2.183 4.262 0.856 1.739 0.314 0.838 µs 12.57 60.25

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 0.171 0.284 0.382 1.021 2.309 2.817 6.665 1.927 2.533 0.606 1.145 ppb 4.38 13.46

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 -10.434 -4.647 -3.537 -0.578 4.888 6.199 18.230 8.425 10.846 2.653 -0.001 µs -3.424 7.458

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 128.101.101.101

peer offset 128.101.101.101 plot

Percentiles...... Ranges...... Skew- Kurt-
Name Min1%5%50%95% 99%Max   90%98%StdDev  MeanUnits nessosis
Server Offset 128.101.101.101 -82.414 -39.026 -15.793 41.467 107.487 148.513 199.969 123.280 187.539 37.047 42.430 µs 0.8348 4.292

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 128.138.141.177

peer offset 128.138.141.177 plot

Percentiles...... Ranges...... Skew- Kurt-
Name Min1%5%50%95% 99%Max   90%98%StdDev  MeanUnits nessosis
Server Offset 128.138.141.177 -631.172 -228.578 -118.083 22.505 349.776 536.390 806.966 467.859 764.968 151.944 56.375 µs -1.164 5.464

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 209.87.233.53

peer offset 209.87.233.53 plot

Percentiles...... Ranges...... Skew- Kurt-
Name Min1%5%50%95% 99%Max   90%98%StdDev  MeanUnits nessosis
Server Offset 209.87.233.53 -10.846 -5.136 -2.151 1.359 3.551 4.973 10.869 5.702 10.109 1.860 1.149 ms -2.187 10.1

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::2 (time2.mbix.ca)

peer offset 2602:fd53:11e:123::2 plot

Percentiles...... Ranges...... Skew- Kurt-
Name Min1%5%50%95% 99%Max   90%98%StdDev  MeanUnits nessosis
Server Offset 2602:fd53:11e:123::2 (time2.mbix.ca) -119.164 -87.814 -71.920 -34.825 -3.425 7.191 26.910 68.495 95.005 20.900 -36.176 µs -28.84 106.4

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) -195.988 -164.415 -129.732 5.507 164.562 266.989 399.215 294.294 431.404 88.198 7.645 µs -2.815 7.438

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) -499.091 -340.134 -253.794 19.809 187.262 335.382 442.715 441.056 675.516 125.905 14.422 µs -3.762 11.44

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:f128:1:3::dd1

peer offset 2607:f128:1:3::dd1 plot

Percentiles...... Ranges...... Skew- Kurt-
Name Min1%5%50%95% 99%Max   90%98%StdDev  MeanUnits nessosis
Server Offset 2607:f128:1:3::dd1 -328.607 -298.378 -277.856 -237.583 -196.028 -179.929 -156.178 81.828 118.449 25.455 -237.182 µs -1129 1.198e+04

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) -552.616 -506.441 -434.485 -372.250 -309.469 -253.737 -210.861 125.016 252.704 40.887 -372.737 µs -1066 1.11e+04

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) -10.435 -4.648 -3.538 -0.579 4.889 6.200 18.231 8.427 10.848 2.653 -0.001 µs -3.425 7.458

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 128.101.101.101

peer jitter 128.101.101.101 plot

Percentiles...... Ranges...... Skew- Kurt-
Name Min1%5%50%95% 99%Max   90%98%StdDev  MeanUnits nessosis
Server Jitter 128.101.101.101 3.939 7.888 10.588 22.599 51.154 66.309 84.722 40.566 58.421 12.651 25.650 µs 5.444 17.64

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 128.138.141.177

peer jitter 128.138.141.177 plot

Percentiles...... Ranges...... Skew- Kurt-
Name Min1%5%50%95% 99%Max   90%98%StdDev  MeanUnits nessosis
Server Jitter 128.138.141.177 0.113 0.269 0.371 0.619 0.878 1.019 2.721 0.507 0.750 0.180 0.625 ms 25.72 140.1

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 209.87.233.53

peer jitter 209.87.233.53 plot

Percentiles...... Ranges...... Skew- Kurt-
Name Min1%5%50%95% 99%Max   90%98%StdDev  MeanUnits nessosis
Server Jitter 209.87.233.53 0.951 2.499 4.309 11.391 30.483 45.255 103.596 26.174 42.756 9.080 13.661 ms 4.456 26.01

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::2 (time2.mbix.ca)

peer jitter 2602:fd53:11e:123::2 plot

Percentiles...... Ranges...... Skew- Kurt-
Name Min1%5%50%95% 99%Max   90%98%StdDev  MeanUnits nessosis
Server Jitter 2602:fd53:11e:123::2 (time2.mbix.ca) 7.713 11.637 14.498 26.346 50.380 72.385 1,243.762 35.882 60.748 42.541 30.640 µs 22.7 622.2

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) 5.412 9.632 12.493 31.371 106.079 162.494 262.227 93.586 152.862 30.560 40.487 µs 3.384 14.75

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) 5.659 8.639 12.449 32.050 122.690 204.770 608.882 110.241 196.131 45.538 45.537 µs 5.072 48.05

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:f128:1:3::dd1

peer jitter 2607:f128:1:3::dd1 plot

Percentiles...... Ranges...... Skew- Kurt-
Name Min1%5%50%95% 99%Max   90%98%StdDev  MeanUnits nessosis
Server Jitter 2607:f128:1:3::dd1 7.024 13.358 17.829 33.364 61.954 80.425 411.782 44.125 67.067 19.753 36.043 µs 12.83 212.4

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) 4.565 8.955 11.730 23.597 47.570 82.978 498.658 35.840 74.023 31.386 28.153 µs 8.611 90.88

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 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) 0.113 0.298 0.405 0.822 1.875 2.748 8.637 1.470 2.450 0.523 0.948 µs 5.706 32.17

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 17.251 17.322 17.385 17.495 17.587 17.610 17.634 0.203 0.287 0.062 17.493 ppm 2.258e+07 6.381e+09
Local Clock Time Offset -10.434 -4.647 -3.537 -0.578 4.888 6.199 18.230 8.425 10.846 2.653 -0.001 µs -3.424 7.458
Local RMS Frequency Jitter 0.171 0.284 0.382 1.021 2.309 2.817 6.665 1.927 2.533 0.606 1.145 ppb 4.38 13.46
Local RMS Time Jitter 0.300 0.444 0.522 0.772 1.378 2.183 4.262 0.856 1.739 0.314 0.838 µs 12.57 60.25
Server Jitter 128.101.101.101 3.939 7.888 10.588 22.599 51.154 66.309 84.722 40.566 58.421 12.651 25.650 µs 5.444 17.64
Server Jitter 128.138.141.177 0.113 0.269 0.371 0.619 0.878 1.019 2.721 0.507 0.750 0.180 0.625 ms 25.72 140.1
Server Jitter 209.87.233.53 0.951 2.499 4.309 11.391 30.483 45.255 103.596 26.174 42.756 9.080 13.661 ms 4.456 26.01
Server Jitter 2602:fd53:11e:123::2 (time2.mbix.ca) 7.713 11.637 14.498 26.346 50.380 72.385 1,243.762 35.882 60.748 42.541 30.640 µs 22.7 622.2
Server Jitter 2606:4700:f1::1 (time.cloudflare.com) 5.412 9.632 12.493 31.371 106.079 162.494 262.227 93.586 152.862 30.560 40.487 µs 3.384 14.75
Server Jitter 2606:4700:f1::123 (time.cloudflare.com) 5.659 8.639 12.449 32.050 122.690 204.770 608.882 110.241 196.131 45.538 45.537 µs 5.072 48.05
Server Jitter 2607:f128:1:3::dd1 7.024 13.358 17.829 33.364 61.954 80.425 411.782 44.125 67.067 19.753 36.043 µs 12.83 212.4
Server Jitter 2607:f388::123:1 (ntp1.doit.wisc.edu) 4.565 8.955 11.730 23.597 47.570 82.978 498.658 35.840 74.023 31.386 28.153 µs 8.611 90.88
Server Jitter PPS(0) 0.113 0.298 0.405 0.822 1.875 2.748 8.637 1.470 2.450 0.523 0.948 µs 5.706 32.17
Server Offset 128.101.101.101 -82.414 -39.026 -15.793 41.467 107.487 148.513 199.969 123.280 187.539 37.047 42.430 µs 0.8348 4.292
Server Offset 128.138.141.177 -631.172 -228.578 -118.083 22.505 349.776 536.390 806.966 467.859 764.968 151.944 56.375 µs -1.164 5.464
Server Offset 209.87.233.53 -10.846 -5.136 -2.151 1.359 3.551 4.973 10.869 5.702 10.109 1.860 1.149 ms -2.187 10.1
Server Offset 2602:fd53:11e:123::2 (time2.mbix.ca) -119.164 -87.814 -71.920 -34.825 -3.425 7.191 26.910 68.495 95.005 20.900 -36.176 µs -28.84 106.4
Server Offset 2606:4700:f1::1 (time.cloudflare.com) -195.988 -164.415 -129.732 5.507 164.562 266.989 399.215 294.294 431.404 88.198 7.645 µs -2.815 7.438
Server Offset 2606:4700:f1::123 (time.cloudflare.com) -499.091 -340.134 -253.794 19.809 187.262 335.382 442.715 441.056 675.516 125.905 14.422 µs -3.762 11.44
Server Offset 2607:f128:1:3::dd1 -328.607 -298.378 -277.856 -237.583 -196.028 -179.929 -156.178 81.828 118.449 25.455 -237.182 µs -1129 1.198e+04
Server Offset 2607:f388::123:1 (ntp1.doit.wisc.edu) -552.616 -506.441 -434.485 -372.250 -309.469 -253.737 -210.861 125.016 252.704 40.887 -372.737 µs -1066 1.11e+04
Server Offset PPS(0) -10.435 -4.648 -3.538 -0.579 4.889 6.200 18.231 8.427 10.848 2.653 -0.001 µs -3.425 7.458
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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