NTPsec

crane3.services.mbix.ca

Report generated: Wed Jul 1 15:53:09 2026 UTC
Start Time: Tue Jun 30 15:53:09 2026 UTC
End Time: Wed Jul 1 15:53:09 2026 UTC
Report Period: 1.0 days

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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 -23.831 -17.949 -3.410 28.225 38.578 67.208 46.174 62.409 14.108 0.028 µs -3.124 7.02
Local Clock Frequency Offset 78.412 78.430 78.449 78.612 78.691 78.709 78.754 0.242 0.280 0.081 78.593 ppm 9.11e+08 8.831e+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 9.357 11.375 18.459 26.586 30.416 37.722 15.211 21.059 4.623 18.658 µs 37.38 147

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 2.324 3.529 4.283 6.630 9.279 10.962 16.714 4.996 7.433 1.573 6.707 ppb 45.11 188.8

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 -23.831 -17.949 -3.410 28.225 38.578 67.208 46.174 62.409 14.108 0.028 µs -3.124 7.02

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 78.430 78.449 78.612 78.691 78.709 78.754 0.242 0.280 0.081 78.593 ppm 9.11e+08 8.831e+11
Temp LM0 37.000 37.000 38.000 39.000 41.000 41.000 42.000 3.000 4.000 0.823 39.420 °C
Temp LM1 35.000 35.000 36.000 37.000 39.000 39.000 39.000 3.000 4.000 0.889 37.196 °C
Temp LM10 32.000 32.000 33.000 34.000 35.000 36.000 36.000 2.000 4.000 0.789 33.854 °C
Temp LM2 33.000 33.000 34.000 35.000 37.000 37.000 38.000 3.000 4.000 0.949 35.214 °C
Temp LM3 37.000 37.000 38.000 39.000 41.000 41.000 42.000 3.000 4.000 0.862 39.391 °C
Temp LM4 35.000 35.000 36.000 37.000 38.000 39.000 39.000 2.000 4.000 0.843 36.783 °C
Temp LM5 62.000 62.000 62.000 63.000 63.000 64.000 64.000 1.000 2.000 0.505 62.808 °C
Temp LM6 39.000 39.000 40.000 41.000 42.000 42.000 43.000 2.000 3.000 0.740 40.819 °C
Temp LM7 37.000 38.000 38.000 39.000 41.000 41.000 42.000 3.000 3.000 0.872 39.448 °C
Temp LM8 38.000 38.000 39.000 40.000 42.000 42.000 42.000 3.000 4.000 0.933 40.164 °C
Temp LM9 36.000 37.000 37.000 39.000 40.000 41.000 41.000 3.000 4.000 0.865 38.669 °C
Temp ZONE0 39.000 39.000 40.000 41.000 42.000 43.000 44.000 2.000 4.000 0.829 40.900 °C
Temp ZONE1 37.000 38.000 38.000 39.000 41.000 41.000 42.000 3.000 3.000 0.905 39.477 °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 1.981 2.007 2.031 2.101 2.172 2.202 2.254 0.141 0.194 0.042 2.100 ms 1.204e+05 5.951e+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 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 -48.845 -43.268 -30.750 2.981 48.308 79.375 80.356 79.058 122.643 24.345 5.643 µs -2.237 5.461

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 22.649 38.410 362.338 396.641 412.569 419.135 358.231 389.920 212.096 312.997 µs -9.26 134.6

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 1.435 1.442 1.456 1.487 2.069 2.088 2.097 0.613 0.646 0.229 1.595 ms 231.3 1516

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) -2.039 -1.717 -1.640 -1.439 -1.207 -0.902 -0.603 0.433 0.816 0.159 -1.424 ms -1020 1.046e+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) -0.540 -0.428 -0.320 1.152 4.806 6.720 8.788 5.126 7.149 1.608 1.514 ms 1.022 4.391

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 -23.832 -17.950 -3.411 28.226 38.579 67.209 46.176 62.411 14.109 0.028 µs -3.124 7.02

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 0.031 0.042 0.060 0.290 0.777 2.338 2.362 0.717 2.296 0.387 0.371 ms 3.304 16.42

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 10.979 14.495 19.704 39.835 136.410 438.778 567.227 116.706 424.283 72.387 55.686 µs 4.294 25.09

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) 0.007 0.009 0.011 0.021 0.042 1.229 2.815 0.031 1.220 0.191 0.040 ms 9.296 128.5

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 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 6.551 7.925 11.044 339.813 580.337 595.166 625.894 569.293 587.241 237.815 274.011 µs 0.4499 1.311

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) 10.369 12.580 16.514 40.379 282.174 594.985 791.196 265.660 582.405 96.337 67.403 µs 3.372 19.32

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) 4.239 5.369 6.717 14.133 24.652 34.066 36.702 17.935 28.697 5.617 14.480 ms 9.536 31.03

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) 1.863 5.398 7.718 17.347 34.512 44.263 73.377 26.794 38.865 8.302 18.735 µs 6.805 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.



Summary


Percentiles...... Ranges...... Skew- Kurt-
Name Min1%5%50%95% 99%Max   90%98%StdDev  MeanUnits nessosis
Local Clock Frequency Offset 78.412 78.430 78.449 78.612 78.691 78.709 78.754 0.242 0.280 0.081 78.593 ppm 9.11e+08 8.831e+11
Local Clock Time Offset -51.536 -23.831 -17.949 -3.410 28.225 38.578 67.208 46.174 62.409 14.108 0.028 µs -3.124 7.02
Local RMS Frequency Jitter 2.324 3.529 4.283 6.630 9.279 10.962 16.714 4.996 7.433 1.573 6.707 ppb 45.11 188.8
Local RMS Time Jitter 5.428 9.357 11.375 18.459 26.586 30.416 37.722 15.211 21.059 4.623 18.658 µs 37.38 147
Server Jitter 132.246.11.227 0.031 0.042 0.060 0.290 0.777 2.338 2.362 0.717 2.296 0.387 0.371 ms 3.304 16.42
Server Jitter 142.3.100.2 10.979 14.495 19.704 39.835 136.410 438.778 567.227 116.706 424.283 72.387 55.686 µs 4.294 25.09
Server Jitter 2600:2600::199 (ntp2.wiktel.com) 0.007 0.009 0.011 0.021 0.042 1.229 2.815 0.031 1.220 0.191 0.040 ms 9.296 128.5
Server Jitter 2602:fde5:2a::13 6.551 7.925 11.044 339.813 580.337 595.166 625.894 569.293 587.241 237.815 274.011 µs 0.4499 1.311
Server Jitter 2606:4700:f1::1 (time.cloudflare.com) 10.369 12.580 16.514 40.379 282.174 594.985 791.196 265.660 582.405 96.337 67.403 µs 3.372 19.32
Server Jitter 2607:f388::123:1 (ntp1.doit.wisc.edu) 4.239 5.369 6.717 14.133 24.652 34.066 36.702 17.935 28.697 5.617 14.480 ms 9.536 31.03
Server Jitter PPS(0) 1.863 5.398 7.718 17.347 34.512 44.263 73.377 26.794 38.865 8.302 18.735 µs 6.805 22
Server Offset 132.246.11.227 1.981 2.007 2.031 2.101 2.172 2.202 2.254 0.141 0.194 0.042 2.100 ms 1.204e+05 5.951e+06
Server Offset 142.3.100.2 -48.845 -43.268 -30.750 2.981 48.308 79.375 80.356 79.058 122.643 24.345 5.643 µs -2.237 5.461
Server Offset 2600:2600::199 (ntp2.wiktel.com) -2,772.580 22.649 38.410 362.338 396.641 412.569 419.135 358.231 389.920 212.096 312.997 µs -9.26 134.6
Server Offset 2602:fde5:2a::13 1.435 1.442 1.456 1.487 2.069 2.088 2.097 0.613 0.646 0.229 1.595 ms 231.3 1516
Server Offset 2606:4700:f1::1 (time.cloudflare.com) -2.039 -1.717 -1.640 -1.439 -1.207 -0.902 -0.603 0.433 0.816 0.159 -1.424 ms -1020 1.046e+04
Server Offset 2607:f388::123:1 (ntp1.doit.wisc.edu) -0.540 -0.428 -0.320 1.152 4.806 6.720 8.788 5.126 7.149 1.608 1.514 ms 1.022 4.391
Server Offset PPS(0) -51.537 -23.832 -17.950 -3.411 28.226 38.579 67.209 46.176 62.411 14.109 0.028 µs -3.124 7.02
Temp LM0 37.000 37.000 38.000 39.000 41.000 41.000 42.000 3.000 4.000 0.823 39.420 °C
Temp LM1 35.000 35.000 36.000 37.000 39.000 39.000 39.000 3.000 4.000 0.889 37.196 °C
Temp LM10 32.000 32.000 33.000 34.000 35.000 36.000 36.000 2.000 4.000 0.789 33.854 °C
Temp LM2 33.000 33.000 34.000 35.000 37.000 37.000 38.000 3.000 4.000 0.949 35.214 °C
Temp LM3 37.000 37.000 38.000 39.000 41.000 41.000 42.000 3.000 4.000 0.862 39.391 °C
Temp LM4 35.000 35.000 36.000 37.000 38.000 39.000 39.000 2.000 4.000 0.843 36.783 °C
Temp LM5 62.000 62.000 62.000 63.000 63.000 64.000 64.000 1.000 2.000 0.505 62.808 °C
Temp LM6 39.000 39.000 40.000 41.000 42.000 42.000 43.000 2.000 3.000 0.740 40.819 °C
Temp LM7 37.000 38.000 38.000 39.000 41.000 41.000 42.000 3.000 3.000 0.872 39.448 °C
Temp LM8 38.000 38.000 39.000 40.000 42.000 42.000 42.000 3.000 4.000 0.933 40.164 °C
Temp LM9 36.000 37.000 37.000 39.000 40.000 41.000 41.000 3.000 4.000 0.865 38.669 °C
Temp ZONE0 39.000 39.000 40.000 41.000 42.000 43.000 44.000 2.000 4.000 0.829 40.900 °C
Temp ZONE1 37.000 38.000 38.000 39.000 41.000 41.000 42.000 3.000 3.000 0.905 39.477 °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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