NTPsec

ntp1.wiktel.com

Report generated: Mon Oct 20 04:53:01 2025 UTC
Start Time: Sun Oct 19 04:53:01 2025 UTC
End Time: Mon Oct 20 04:53:01 2025 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 -8.982 -3.996 -3.167 -0.840 4.731 5.500 6.531 7.898 9.496 2.625 -0.008 µs -3.471 7.005
Local Clock Frequency Offset 17.434 17.457 17.493 17.554 17.619 17.631 17.637 0.126 0.174 0.042 17.554 ppm 7.321e+07 3.063e+10

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 0.303 0.413 0.477 0.686 1.475 2.144 3.255 0.998 1.731 0.330 0.774 µs 9.099 39.91

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 0.231 0.378 0.501 1.122 2.206 2.471 2.709 1.705 2.093 0.500 1.181 ppb 7.307 21.33

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 -8.982 -3.996 -3.167 -0.840 4.731 5.500 6.531 7.898 9.496 2.625 -0.008 µs -3.471 7.005

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 -45.741 -37.152 0.137 44.018 94.158 123.118 136.247 94.021 160.270 28.482 44.487 µs 1.993 6.303

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 -715.140 -567.563 -276.402 3.742 352.827 537.504 608.065 629.229 1,105.067 184.895 23.328 µs -3.434 10.99

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 -6.612 -4.834 -2.688 1.184 3.718 4.786 7.294 6.406 9.620 1.909 0.927 ms -2.393 7.641

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) -100.238 -94.849 -77.353 -38.399 -6.333 9.507 12.210 71.020 104.356 21.341 -39.566 µs -32.06 120.9

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) 167.469 202.571 244.262 336.290 476.272 519.324 592.907 232.010 316.753 67.531 350.357 µs 86.51 424.7

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::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) 163.687 163.687 219.573 361.780 479.312 493.689 493.689 259.739 330.002 82.655 349.979 µs 43.25 170.7

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 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 -299.306 -291.301 -274.017 -235.184 -193.919 -172.100 -160.080 80.098 119.201 25.216 -234.801 µs -1127 1.194e+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) -480.292 -479.504 -429.438 -362.449 -306.972 -228.026 -224.949 122.466 251.478 40.153 -362.197 µs -1036 1.068e+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) -8.983 -3.997 -3.168 -0.841 4.732 5.501 6.532 7.900 9.498 2.626 -0.008 µs -3.471 7.006

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 6.640 7.076 9.064 21.493 43.421 53.543 56.942 34.357 46.467 10.452 22.487 µs 5.949 17.9

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 0.200 0.291 0.403 0.630 0.887 1.151 1.347 0.484 0.859 0.156 0.635 ms 38.56 156.5

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 2.641 3.242 5.726 13.376 28.908 35.117 131.094 23.182 31.875 9.329 14.914 ms 8.841 101.8

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::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) 11.118 12.623 16.075 28.181 50.405 60.958 77.308 34.330 48.335 10.691 29.766 µs 12.12 41.84

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.



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) 6.624 7.173 10.955 30.720 98.743 146.995 192.658 87.788 139.822 31.597 41.475 µs 2.706 9.35

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::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) 11.074 11.074 13.195 33.478 103.188 210.282 210.282 89.993 199.208 33.018 41.357 µs 3.836 17.45

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 14.423 15.961 19.357 32.023 63.978 306.874 448.776 44.621 290.913 40.584 38.622 µs 8.218 79.16

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) 8.087 8.988 12.617 23.876 59.970 317.657 385.965 47.353 308.669 45.857 33.938 µs 4.891 32.61

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) 0.095 0.262 0.366 0.741 1.797 2.883 6.994 1.431 2.621 0.519 0.874 µs 5.243 29.12

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 17.434 17.457 17.493 17.554 17.619 17.631 17.637 0.126 0.174 0.042 17.554 ppm 7.321e+07 3.063e+10
Local Clock Time Offset -8.982 -3.996 -3.167 -0.840 4.731 5.500 6.531 7.898 9.496 2.625 -0.008 µs -3.471 7.005
Local RMS Frequency Jitter 0.231 0.378 0.501 1.122 2.206 2.471 2.709 1.705 2.093 0.500 1.181 ppb 7.307 21.33
Local RMS Time Jitter 0.303 0.413 0.477 0.686 1.475 2.144 3.255 0.998 1.731 0.330 0.774 µs 9.099 39.91
Server Jitter 128.101.101.101 6.640 7.076 9.064 21.493 43.421 53.543 56.942 34.357 46.467 10.452 22.487 µs 5.949 17.9
Server Jitter 128.138.141.177 0.200 0.291 0.403 0.630 0.887 1.151 1.347 0.484 0.859 0.156 0.635 ms 38.56 156.5
Server Jitter 209.87.233.53 2.641 3.242 5.726 13.376 28.908 35.117 131.094 23.182 31.875 9.329 14.914 ms 8.841 101.8
Server Jitter 2602:fd53:11e:123::2 (time2.mbix.ca) 11.118 12.623 16.075 28.181 50.405 60.958 77.308 34.330 48.335 10.691 29.766 µs 12.12 41.84
Server Jitter 2606:4700:f1::1 (time.cloudflare.com) 6.624 7.173 10.955 30.720 98.743 146.995 192.658 87.788 139.822 31.597 41.475 µs 2.706 9.35
Server Jitter 2606:4700:f1::123 (time.cloudflare.com) 11.074 11.074 13.195 33.478 103.188 210.282 210.282 89.993 199.208 33.018 41.357 µs 3.836 17.45
Server Jitter 2607:f128:1:3::dd1 14.423 15.961 19.357 32.023 63.978 306.874 448.776 44.621 290.913 40.584 38.622 µs 8.218 79.16
Server Jitter 2607:f388::123:1 (ntp1.doit.wisc.edu) 8.087 8.988 12.617 23.876 59.970 317.657 385.965 47.353 308.669 45.857 33.938 µs 4.891 32.61
Server Jitter PPS(0) 0.095 0.262 0.366 0.741 1.797 2.883 6.994 1.431 2.621 0.519 0.874 µs 5.243 29.12
Server Offset 128.101.101.101 -45.741 -37.152 0.137 44.018 94.158 123.118 136.247 94.021 160.270 28.482 44.487 µs 1.993 6.303
Server Offset 128.138.141.177 -715.140 -567.563 -276.402 3.742 352.827 537.504 608.065 629.229 1,105.067 184.895 23.328 µs -3.434 10.99
Server Offset 209.87.233.53 -6.612 -4.834 -2.688 1.184 3.718 4.786 7.294 6.406 9.620 1.909 0.927 ms -2.393 7.641
Server Offset 2602:fd53:11e:123::2 (time2.mbix.ca) -100.238 -94.849 -77.353 -38.399 -6.333 9.507 12.210 71.020 104.356 21.341 -39.566 µs -32.06 120.9
Server Offset 2606:4700:f1::1 (time.cloudflare.com) 167.469 202.571 244.262 336.290 476.272 519.324 592.907 232.010 316.753 67.531 350.357 µs 86.51 424.7
Server Offset 2606:4700:f1::123 (time.cloudflare.com) 163.687 163.687 219.573 361.780 479.312 493.689 493.689 259.739 330.002 82.655 349.979 µs 43.25 170.7
Server Offset 2607:f128:1:3::dd1 -299.306 -291.301 -274.017 -235.184 -193.919 -172.100 -160.080 80.098 119.201 25.216 -234.801 µs -1127 1.194e+04
Server Offset 2607:f388::123:1 (ntp1.doit.wisc.edu) -480.292 -479.504 -429.438 -362.449 -306.972 -228.026 -224.949 122.466 251.478 40.153 -362.197 µs -1036 1.068e+04
Server Offset PPS(0) -8.983 -3.997 -3.168 -0.841 4.732 5.501 6.532 7.900 9.498 2.626 -0.008 µs -3.471 7.006
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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