NTPsec

Pi4/Uputronics

Report generated: Thu Jul 2 01:03:03 2020 UTC
Start Time: Wed Jul 1 01:03:01 2020 UTC
End Time: Thu Jul 2 01:03:01 2020 UTC
Report Period: 1.0 days
Warning: plots clipped

Daily stats   Weekly stats   24 Hour Scatter Plots: ( 1   2   )

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 -5.905 -4.180 -3.551 -0.663 4.268 8.268 25.270 7.819 12.448 2.844 -0.050 µs -2.853 10.24
Local Clock Frequency Offset -1.733 -1.723 -1.642 -0.927 -0.415 -0.359 -0.328 1.227 1.364 0.432 -0.982 ppm -45.12 183.5

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 0.052 0.084 0.101 0.177 1.003 1.489 4.669 0.902 1.405 0.329 0.291 µs 4.087 33.53

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 0.046 0.082 0.150 0.571 1.110 1.734 4.170 0.960 1.652 0.344 0.605 ppb 5.562 35.73

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 -5.905 -4.180 -3.551 -0.663 4.268 8.268 25.270 7.819 12.448 2.844 -0.050 µs -2.853 10.24

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 -1.733 -1.723 -1.642 -0.927 -0.415 -0.359 -0.328 1.227 1.364 0.432 -0.982 ppm -45.12 183.5
Temp ZONE0 49.388 49.388 49.926 52.616 55.306 55.844 55.844 5.380 6.456 1.826 52.747 °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.



Local GPS

local gps plot

Percentiles...... Ranges...... Skew- Kurt-
Name Min1%5%50%95% 99%Max   90%98%StdDev  MeanUnits nessosis
nSats 0.000 4.000 5.000 7.000 10.000 10.000 12.000 5.000 6.000 1.398 7.315 nSat 88.45 429.3
TDOP 0.000 0.660 0.770 1.250 2.820 5.220 79.920 2.050 4.560 1.714 1.490 19.7 607.5

Local GPS. The Time Dilution of Precision (TDOP) is plotted in blue. The number of visible satellites (nSat) is plotted in red.

TDOP is field 3, and nSats is field 4, from the gpsd log file. The gpsd log file is created by the ntploggps program.

TDOP is a dimensionless error factor. Smaller numbers are better. TDOP ranges from 1 (ideal), 2 to 5 (good), to greater than 20 (poor). Some GNSS receivers report TDOP less than one which is theoretically impossible.



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 2001:470:e815::23 (pi3.rellim.com)

peer offset 2001:470:e815::23 plot

Percentiles...... Ranges...... Skew- Kurt-
Name Min1%5%50%95% 99%Max   90%98%StdDev  MeanUnits nessosis
Server Offset 2001:470:e815::23 (pi3.rellim.com) -104.323 -59.038 -40.342 -18.368 53.325 69.982 83.547 93.667 129.020 29.137 -9.161 µs -5.163 11.69

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 2001:470:e815::25 (pi5.rellim.com)

peer offset 2001:470:e815::25 plot

Percentiles...... Ranges...... Skew- Kurt-
Name Min1%5%50%95% 99%Max   90%98%StdDev  MeanUnits nessosis
Server Offset 2001:470:e815::25 (pi5.rellim.com) -115.980 -105.213 -97.891 -68.398 -13.561 7.741 66.157 84.330 112.954 28.924 -60.209 µs -37.89 142.5

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 2001:470:e815::8 (spidey.rellim.com)

peer offset 2001:470:e815::8 plot

Percentiles...... Ranges...... Skew- Kurt-
Name Min1%5%50%95% 99%Max   90%98%StdDev  MeanUnits nessosis
Server Offset 2001:470:e815::8 (spidey.rellim.com) -117.838 -76.448 -60.676 -22.497 57.900 131.399 246.222 118.576 207.847 40.090 -14.051 µs -4.843 13.62

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 204.17.205.1

peer offset 204.17.205.1 plot

Percentiles...... Ranges...... Skew- Kurt-
Name Min1%5%50%95% 99%Max   90%98%StdDev  MeanUnits nessosis
Server Offset 204.17.205.1 -75.663 -62.184 -51.453 -27.733 38.928 58.194 78.616 90.381 120.378 27.978 -18.894 µs -8.724 21.42

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 204.17.205.27

peer offset 204.17.205.27 plot

Percentiles...... Ranges...... Skew- Kurt-
Name Min1%5%50%95% 99%Max   90%98%StdDev  MeanUnits nessosis
Server Offset 204.17.205.27 -80.243 -77.055 -72.297 -50.009 14.223 30.784 51.445 86.520 107.839 25.503 -43.205 µs -26.37 86.7

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 204.17.205.30

peer offset 204.17.205.30 plot

Percentiles...... Ranges...... Skew- Kurt-
Name Min1%5%50%95% 99%Max   90%98%StdDev  MeanUnits nessosis
Server Offset 204.17.205.30 -76.475 -56.782 -42.450 -13.858 67.885 86.916 91.621 110.335 143.698 33.587 -4.951 µs -3.914 8.224

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(0)

peer offset SHM(0) plot

Percentiles...... Ranges...... Skew- Kurt-
Name Min1%5%50%95% 99%Max   90%98%StdDev  MeanUnits nessosis
Server Offset SHM(0) -650.125 -516.221 -455.397 -365.357 -280.823 -46.029 -22.964 174.573 470.192 64.118 -363.879 ms -316 2226

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) -5.906 -4.181 -3.552 -0.664 4.269 8.269 25.271 7.821 12.450 2.844 -0.050 µs -2.853 10.24

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 2001:470:e815::23 (pi3.rellim.com)

peer jitter 2001:470:e815::23 plot

Percentiles...... Ranges...... Skew- Kurt-
Name Min1%5%50%95% 99%Max   90%98%StdDev  MeanUnits nessosis
Server Jitter 2001:470:e815::23 (pi3.rellim.com) 2.174 2.981 5.176 18.402 76.192 95.064 110.764 71.016 92.083 22.886 26.893 µs 1.869 5.011

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 2001:470:e815::25 (pi5.rellim.com)

peer jitter 2001:470:e815::25 plot

Percentiles...... Ranges...... Skew- Kurt-
Name Min1%5%50%95% 99%Max   90%98%StdDev  MeanUnits nessosis
Server Jitter 2001:470:e815::25 (pi5.rellim.com) 2.447 2.987 6.803 19.589 64.765 79.882 148.806 57.962 76.895 21.028 28.646 µs 2.348 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 2001:470:e815::8 (spidey.rellim.com)

peer jitter 2001:470:e815::8 plot

Percentiles...... Ranges...... Skew- Kurt-
Name Min1%5%50%95% 99%Max   90%98%StdDev  MeanUnits nessosis
Server Jitter 2001:470:e815::8 (spidey.rellim.com) 3.693 6.292 9.524 26.765 87.593 147.052 182.499 78.069 140.760 27.707 34.968 µs 3.073 12.61

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 204.17.205.1

peer jitter 204.17.205.1 plot

Percentiles...... Ranges...... Skew- Kurt-
Name Min1%5%50%95% 99%Max   90%98%StdDev  MeanUnits nessosis
Server Jitter 204.17.205.1 3.738 5.572 8.044 19.188 61.089 82.359 104.883 53.045 76.787 17.266 24.720 µs 3.069 9.835

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 204.17.205.27

peer jitter 204.17.205.27 plot

Percentiles...... Ranges...... Skew- Kurt-
Name Min1%5%50%95% 99%Max   90%98%StdDev  MeanUnits nessosis
Server Jitter 204.17.205.27 1.615 2.625 3.861 14.513 64.746 81.389 97.274 60.885 78.764 18.573 20.114 µs 2.043 6.369

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 204.17.205.30

peer jitter 204.17.205.30 plot

Percentiles...... Ranges...... Skew- Kurt-
Name Min1%5%50%95% 99%Max   90%98%StdDev  MeanUnits nessosis
Server Jitter 204.17.205.30 3.661 6.839 10.587 25.726 72.094 93.236 108.265 61.507 86.397 19.016 30.746 µs 3.472 10.51

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(0)

peer jitter SHM(0) plot

Percentiles...... Ranges...... Skew- Kurt-
Name Min1%5%50%95% 99%Max   90%98%StdDev  MeanUnits nessosis
Server Jitter SHM(0) 4.617 10.855 16.734 35.472 155.759 324.822 473.126 139.025 313.967 51.348 50.332 ms 3.866 22.08

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) 0.025 0.060 0.090 0.331 2.267 5.803 20.883 2.177 5.743 1.075 0.643 µs 5.251 67.88

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.



Summary


Percentiles...... Ranges...... Skew- Kurt-
Name Min1%5%50%95% 99%Max   90%98%StdDev  MeanUnits nessosis
Local Clock Frequency Offset -1.733 -1.723 -1.642 -0.927 -0.415 -0.359 -0.328 1.227 1.364 0.432 -0.982 ppm -45.12 183.5
Local Clock Time Offset -5.905 -4.180 -3.551 -0.663 4.268 8.268 25.270 7.819 12.448 2.844 -0.050 µs -2.853 10.24
Local RMS Frequency Jitter 0.046 0.082 0.150 0.571 1.110 1.734 4.170 0.960 1.652 0.344 0.605 ppb 5.562 35.73
Local RMS Time Jitter 0.052 0.084 0.101 0.177 1.003 1.489 4.669 0.902 1.405 0.329 0.291 µs 4.087 33.53
Server Jitter 2001:470:e815::23 (pi3.rellim.com) 2.174 2.981 5.176 18.402 76.192 95.064 110.764 71.016 92.083 22.886 26.893 µs 1.869 5.011
Server Jitter 2001:470:e815::25 (pi5.rellim.com) 2.447 2.987 6.803 19.589 64.765 79.882 148.806 57.962 76.895 21.028 28.646 µs 2.348 8
Server Jitter 2001:470:e815::8 (spidey.rellim.com) 3.693 6.292 9.524 26.765 87.593 147.052 182.499 78.069 140.760 27.707 34.968 µs 3.073 12.61
Server Jitter 204.17.205.1 3.738 5.572 8.044 19.188 61.089 82.359 104.883 53.045 76.787 17.266 24.720 µs 3.069 9.835
Server Jitter 204.17.205.27 1.615 2.625 3.861 14.513 64.746 81.389 97.274 60.885 78.764 18.573 20.114 µs 2.043 6.369
Server Jitter 204.17.205.30 3.661 6.839 10.587 25.726 72.094 93.236 108.265 61.507 86.397 19.016 30.746 µs 3.472 10.51
Server Jitter SHM(0) 4.617 10.855 16.734 35.472 155.759 324.822 473.126 139.025 313.967 51.348 50.332 ms 3.866 22.08
Server Jitter SHM(1) 0.025 0.060 0.090 0.331 2.267 5.803 20.883 2.177 5.743 1.075 0.643 µs 5.251 67.88
Server Offset 2001:470:e815::23 (pi3.rellim.com) -104.323 -59.038 -40.342 -18.368 53.325 69.982 83.547 93.667 129.020 29.137 -9.161 µs -5.163 11.69
Server Offset 2001:470:e815::25 (pi5.rellim.com) -115.980 -105.213 -97.891 -68.398 -13.561 7.741 66.157 84.330 112.954 28.924 -60.209 µs -37.89 142.5
Server Offset 2001:470:e815::8 (spidey.rellim.com) -117.838 -76.448 -60.676 -22.497 57.900 131.399 246.222 118.576 207.847 40.090 -14.051 µs -4.843 13.62
Server Offset 204.17.205.1 -75.663 -62.184 -51.453 -27.733 38.928 58.194 78.616 90.381 120.378 27.978 -18.894 µs -8.724 21.42
Server Offset 204.17.205.27 -80.243 -77.055 -72.297 -50.009 14.223 30.784 51.445 86.520 107.839 25.503 -43.205 µs -26.37 86.7
Server Offset 204.17.205.30 -76.475 -56.782 -42.450 -13.858 67.885 86.916 91.621 110.335 143.698 33.587 -4.951 µs -3.914 8.224
Server Offset SHM(0) -650.125 -516.221 -455.397 -365.357 -280.823 -46.029 -22.964 174.573 470.192 64.118 -363.879 ms -316 2226
Server Offset SHM(1) -5.906 -4.181 -3.552 -0.664 4.269 8.269 25.271 7.821 12.450 2.844 -0.050 µs -2.853 10.24
TDOP 0.000 0.660 0.770 1.250 2.820 5.220 79.920 2.050 4.560 1.714 1.490 19.7 607.5
Temp ZONE0 49.388 49.388 49.926 52.616 55.306 55.844 55.844 5.380 6.456 1.826 52.747 °C
nSats 0.000 4.000 5.000 7.000 10.000 10.000 12.000 5.000 6.000 1.398 7.315 nSat 88.45 429.3
Summary as CSV file


This server:

Motherboard: Raspberry Pi 3
OS: Gentoo stable
GPS; Adafruit GPS HAT
GPS/PPS server: gpsd
NTP server: NTPsec
../ntp.conf

Notes:

22:00 29 Nov 2017 SD card crash, start over

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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