NTPsec

Backup/Meinberg

Report generated: Mon Sep 15 10:33:01 2025 UTC
Start Time: Sun Sep 14 10:33:00 2025 UTC
End Time: Mon Sep 15 10:33:00 2025 UTC
Report Period: 1.0 days
Warning: plots clipped

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 -18.194 -16.850 -15.019 -5.979 8.196 9.565 10.898 23.215 26.415 7.447 -4.568 µs 0.2789 1.886
Local Clock Frequency Offset 11.935 11.944 11.980 12.069 12.273 12.304 12.310 0.293 0.360 0.085 12.081 ppm 0.9807 3.453

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 0.418 0.476 0.550 0.757 1.153 1.554 1.783 0.603 1.078 0.195 0.787 µs 1.547 7.002

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 78.000 88.000 124.000 459.000 886.000 976.000 1,009.000 762.000 888.000 238.961 477.483 10e-12 0.2348 2.027

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 -18.194 -16.850 -15.019 -5.979 8.196 9.565 10.898 23.215 26.415 7.447 -4.568 µs 0.2789 1.886

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 11.935 11.944 11.980 12.069 12.273 12.304 12.310 0.293 0.360 0.085 12.081 ppm 0.9807 3.453
Temp /dev/sda 45.000 45.000 46.000 46.000 47.000 47.000 47.000 1.000 2.000 0.303 46.068 °C
Temp /dev/sdb 56.000 56.000 56.000 57.000 58.000 59.000 59.000 2.000 3.000 0.849 56.954 °C
Temp /dev/sdc 56.000 56.000 56.000 58.000 58.000 58.000 58.000 2.000 2.000 0.548 57.836 °C
Temp /dev/sdd 62.000 62.000 62.000 64.000 64.000 64.000 64.000 2.000 2.000 0.758 63.345 °C
Temp /dev/sde 46.000 46.000 46.000 47.000 48.000 48.000 48.000 2.000 2.000 0.511 47.050 °C
Temp /dev/sdf 56.000 56.000 56.000 57.000 58.000 58.000 58.000 2.000 2.000 0.640 56.822 °C
Temp LM0 28.750 28.750 29.000 29.750 30.250 30.500 30.500 1.250 1.750 0.367 29.647 °C
Temp LM1 40.500 40.500 41.000 41.500 42.000 42.000 42.500 1.000 1.500 0.372 41.379 °C
Temp LM10 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 °C
Temp LM11 0.000 0.000 0.000 0.000 0.000 0.000 46.000 0.000 0.000 3.867 0.327 °C
Temp LM12 27.800 45.000 46.000 46.000 47.000 47.000 47.000 1.000 2.000 1.566 45.935 °C
Temp LM13 27.800 27.800 27.800 27.800 27.800 27.800 29.800 0.000 0.000 0.168 27.814 °C
Temp LM14 29.800 29.800 29.800 29.800 29.800 29.800 31.250 0.000 0.000 0.122 29.810 °C
Temp LM15 30.000 30.250 30.250 31.000 31.500 32.000 57.000 1.250 1.750 2.224 31.100 °C
Temp LM16 56.000 56.000 56.000 57.000 58.000 58.000 62.000 2.000 2.000 0.834 57.036 °C
Temp LM17 60.500 61.000 61.000 61.500 62.500 62.500 64.000 1.500 1.500 0.484 61.459 °C
Temp LM18 57.000 62.000 63.000 64.000 64.000 64.000 64.000 1.000 2.000 0.792 63.512 °C
Temp LM19 29.000 56.000 56.000 57.000 58.000 59.000 60.000 2.000 3.000 2.455 56.879 °C
Temp LM2 34.000 46.000 46.000 47.000 48.000 48.000 48.000 2.000 2.000 1.201 46.964 °C
Temp LM20 27.000 28.000 28.000 29.000 30.000 31.000 31.000 2.000 3.000 0.730 29.274 °C
Temp LM21 27.000 27.000 28.000 29.000 30.000 31.000 31.000 2.000 4.000 0.829 29.050 °C
Temp LM22 25.000 25.000 25.000 27.000 28.000 29.000 29.000 3.000 4.000 0.846 26.662 °C
Temp LM23 26.000 26.000 27.000 28.000 29.000 30.000 30.000 2.000 4.000 0.861 28.053 °C
Temp LM24 27.000 27.000 27.000 29.000 30.000 30.000 31.000 3.000 3.000 0.828 28.541 °C
Temp LM3 32.500 33.000 33.000 34.000 35.000 35.000 35.000 2.000 2.000 0.432 33.948 °C
Temp LM4 24.000 31.500 31.500 32.500 33.000 33.500 33.500 1.500 2.000 0.855 32.411 °C
Temp LM5 24.000 24.000 24.000 24.000 24.000 24.000 29.500 0.000 0.000 0.442 24.037 °C
Temp LM6 27.000 27.500 28.000 29.000 29.500 30.000 62.000 1.500 2.500 2.838 29.036 °C
Temp LM7 0.000 60.000 61.000 61.000 62.000 62.000 62.000 1.000 2.000 5.162 60.776 °C
Temp LM8 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 °C
Temp LM9 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 °C
Temp ZONE0 27.000 27.000 28.000 29.000 30.000 31.000 31.000 2.000 4.000 0.752 29.082 °C
Temp ZONE1 27.800 27.800 27.800 27.800 27.800 27.800 27.800 0.000 0.000 0.000 27.800 °C
Temp ZONE2 60.500 61.000 61.000 61.500 62.500 62.500 62.500 1.500 1.500 0.459 61.438 °C
Temp ZONE3 29.800 29.800 29.800 29.800 29.800 29.800 29.800 0.000 0.000 0.000 29.800 °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 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) -73.050 -43.011 -15.128 33.072 85.252 107.224 120.007 100.380 150.235 32.097 34.858 µs -0.09094 2.88

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 -1.160 -1.120 -1.030 -0.488 0.015 0.082 0.130 1.045 1.202 0.338 -0.495 ms -0.05344 1.883

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 204.17.205.24

peer offset 204.17.205.24 plot

Percentiles...... Ranges...... Skew- Kurt-
Name Min1%5%50%95% 99%Max   90%98%StdDev  MeanUnits nessosis
Server Offset 204.17.205.24 -49.990 -35.526 -10.475 30.358 63.743 73.064 88.911 74.218 108.590 21.491 29.459 µs -0.5336 4.067

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) -18.195 -16.851 -15.020 -5.980 8.197 9.566 10.899 23.217 26.417 7.448 -4.569 µs 0.279 1.886

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::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) 1.795 3.895 5.592 27.040 78.179 101.540 120.747 72.587 97.645 23.756 32.720 µs 0.9553 3.459

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 4.576 6.329 7.746 14.861 33.426 54.965 72.305 25.680 48.636 8.907 17.068 µs 2.066 9.382

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 204.17.205.24

peer jitter 204.17.205.24 plot

Percentiles...... Ranges...... Skew- Kurt-
Name Min1%5%50%95% 99%Max   90%98%StdDev  MeanUnits nessosis
Server Jitter 204.17.205.24 1.188 1.946 3.361 11.707 44.337 66.202 97.895 40.976 64.256 13.940 16.076 µs 1.956 8.172

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) 0.237 0.332 0.524 1.512 3.976 5.430 7.683 3.452 5.098 1.118 1.792 µs 1.35 5.144

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.



Summary


Percentiles...... Ranges...... Skew- Kurt-
Name Min1%5%50%95% 99%Max   90%98%StdDev  MeanUnits nessosis
Local Clock Frequency Offset 11.935 11.944 11.980 12.069 12.273 12.304 12.310 0.293 0.360 0.085 12.081 ppm 0.9807 3.453
Local Clock Time Offset -18.194 -16.850 -15.019 -5.979 8.196 9.565 10.898 23.215 26.415 7.447 -4.568 µs 0.2789 1.886
Local RMS Frequency Jitter 78.000 88.000 124.000 459.000 886.000 976.000 1,009.000 762.000 888.000 238.961 477.483 10e-12 0.2348 2.027
Local RMS Time Jitter 0.418 0.476 0.550 0.757 1.153 1.554 1.783 0.603 1.078 0.195 0.787 µs 1.547 7.002
Server Jitter 2001:470:e815::8 (spidey.rellim.com) 1.795 3.895 5.592 27.040 78.179 101.540 120.747 72.587 97.645 23.756 32.720 µs 0.9553 3.459
Server Jitter 204.17.205.1 4.576 6.329 7.746 14.861 33.426 54.965 72.305 25.680 48.636 8.907 17.068 µs 2.066 9.382
Server Jitter 204.17.205.24 1.188 1.946 3.361 11.707 44.337 66.202 97.895 40.976 64.256 13.940 16.076 µs 1.956 8.172
Server Jitter SHM(0) 0.237 0.332 0.524 1.512 3.976 5.430 7.683 3.452 5.098 1.118 1.792 µs 1.35 5.144
Server Offset 2001:470:e815::8 (spidey.rellim.com) -73.050 -43.011 -15.128 33.072 85.252 107.224 120.007 100.380 150.235 32.097 34.858 µs -0.09094 2.88
Server Offset 204.17.205.1 -1.160 -1.120 -1.030 -0.488 0.015 0.082 0.130 1.045 1.202 0.338 -0.495 ms -0.05344 1.883
Server Offset 204.17.205.24 -49.990 -35.526 -10.475 30.358 63.743 73.064 88.911 74.218 108.590 21.491 29.459 µs -0.5336 4.067
Server Offset SHM(0) -18.195 -16.851 -15.020 -5.980 8.197 9.566 10.899 23.217 26.417 7.448 -4.569 µs 0.279 1.886
Temp /dev/sda 45.000 45.000 46.000 46.000 47.000 47.000 47.000 1.000 2.000 0.303 46.068 °C
Temp /dev/sdb 56.000 56.000 56.000 57.000 58.000 59.000 59.000 2.000 3.000 0.849 56.954 °C
Temp /dev/sdc 56.000 56.000 56.000 58.000 58.000 58.000 58.000 2.000 2.000 0.548 57.836 °C
Temp /dev/sdd 62.000 62.000 62.000 64.000 64.000 64.000 64.000 2.000 2.000 0.758 63.345 °C
Temp /dev/sde 46.000 46.000 46.000 47.000 48.000 48.000 48.000 2.000 2.000 0.511 47.050 °C
Temp /dev/sdf 56.000 56.000 56.000 57.000 58.000 58.000 58.000 2.000 2.000 0.640 56.822 °C
Temp LM0 28.750 28.750 29.000 29.750 30.250 30.500 30.500 1.250 1.750 0.367 29.647 °C
Temp LM1 40.500 40.500 41.000 41.500 42.000 42.000 42.500 1.000 1.500 0.372 41.379 °C
Temp LM10 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 °C
Temp LM11 0.000 0.000 0.000 0.000 0.000 0.000 46.000 0.000 0.000 3.867 0.327 °C
Temp LM12 27.800 45.000 46.000 46.000 47.000 47.000 47.000 1.000 2.000 1.566 45.935 °C
Temp LM13 27.800 27.800 27.800 27.800 27.800 27.800 29.800 0.000 0.000 0.168 27.814 °C
Temp LM14 29.800 29.800 29.800 29.800 29.800 29.800 31.250 0.000 0.000 0.122 29.810 °C
Temp LM15 30.000 30.250 30.250 31.000 31.500 32.000 57.000 1.250 1.750 2.224 31.100 °C
Temp LM16 56.000 56.000 56.000 57.000 58.000 58.000 62.000 2.000 2.000 0.834 57.036 °C
Temp LM17 60.500 61.000 61.000 61.500 62.500 62.500 64.000 1.500 1.500 0.484 61.459 °C
Temp LM18 57.000 62.000 63.000 64.000 64.000 64.000 64.000 1.000 2.000 0.792 63.512 °C
Temp LM19 29.000 56.000 56.000 57.000 58.000 59.000 60.000 2.000 3.000 2.455 56.879 °C
Temp LM2 34.000 46.000 46.000 47.000 48.000 48.000 48.000 2.000 2.000 1.201 46.964 °C
Temp LM20 27.000 28.000 28.000 29.000 30.000 31.000 31.000 2.000 3.000 0.730 29.274 °C
Temp LM21 27.000 27.000 28.000 29.000 30.000 31.000 31.000 2.000 4.000 0.829 29.050 °C
Temp LM22 25.000 25.000 25.000 27.000 28.000 29.000 29.000 3.000 4.000 0.846 26.662 °C
Temp LM23 26.000 26.000 27.000 28.000 29.000 30.000 30.000 2.000 4.000 0.861 28.053 °C
Temp LM24 27.000 27.000 27.000 29.000 30.000 30.000 31.000 3.000 3.000 0.828 28.541 °C
Temp LM3 32.500 33.000 33.000 34.000 35.000 35.000 35.000 2.000 2.000 0.432 33.948 °C
Temp LM4 24.000 31.500 31.500 32.500 33.000 33.500 33.500 1.500 2.000 0.855 32.411 °C
Temp LM5 24.000 24.000 24.000 24.000 24.000 24.000 29.500 0.000 0.000 0.442 24.037 °C
Temp LM6 27.000 27.500 28.000 29.000 29.500 30.000 62.000 1.500 2.500 2.838 29.036 °C
Temp LM7 0.000 60.000 61.000 61.000 62.000 62.000 62.000 1.000 2.000 5.162 60.776 °C
Temp LM8 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 °C
Temp LM9 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 °C
Temp ZONE0 27.000 27.000 28.000 29.000 30.000 31.000 31.000 2.000 4.000 0.752 29.082 °C
Temp ZONE1 27.800 27.800 27.800 27.800 27.800 27.800 27.800 0.000 0.000 0.000 27.800 °C
Temp ZONE2 60.500 61.000 61.000 61.500 62.500 62.500 62.500 1.500 1.500 0.459 61.438 °C
Temp ZONE3 29.800 29.800 29.800 29.800 29.800 29.800 29.800 0.000 0.000 0.000 29.800 °C
Summary as CSV file


This server:

CPU: Quad core Intel Xeon E3-1241 v3
Kernel: config.gz
Motherboard: Supermicro X10SAE
OS: Gentoo stable
GPS; Meinberg GPS180PEX
GPS/PPS server: gpsd
NTP server: NTPsec
ntp.conf: current
ntp.log: current

Notes:

Notes:
03:20Z 20 Dec 2018 Change poll from 8s to 4s.  4s seems best.
01:30Z 20 Dec 2018 Change poll from 2s to 8s.
23:00Z 20 Dec 2018 Change poll from 4s to 2s.
22:00Z 20 Dec 2018 Change poll from 64s to 4s.
21:40  19 Dec 2018 -- just started

Poll:
64s   SHM(0) offset StdDev 34.5 us, jitter 5.3 us
8s    8s better jitter than 4s, but worse offset than 4s
4s    SHM(0) offset mean 0 ns StdDev 481 ns, jitter 449 ns StdDev 250 ns
      better than 2s, almost unstable
2s

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.
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 FIsher-Pearson moment of skewness. There are other different ways to calculate Skewness Wikipedia describes Skewness best: "The qualitative interpretation of the skew is complicated and unintuitive."
A normal distribution has a skewness of zero.
Kurtosis, Kurt:
The kurtosis of a random variable X is the fourth standardized moment and is a dimension-less ratio. ntpviz uses standard Kurtosis. There are other different ways to calculate 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".
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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