NTPsec

Backup/Meinberg

Report generated: Sun Sep 14 15:43:00 2025 UTC
Start Time: Sun Sep 7 15:43:00 2025 UTC
End Time: Sun Sep 14 15:43:00 2025 UTC
Report Period: 7.0 days

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 -97.171 -41.592 -15.622 -2.218 15.895 75.342 204.015 31.517 116.934 17.964 -0.461 µs 4.014 39.66
Local Clock Frequency Offset 11.771 11.779 11.828 12.128 12.568 12.643 12.649 0.740 0.864 0.227 12.147 ppm 0.3131 2.199

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 0.309 0.429 0.520 0.793 2.340 9.082 17.410 1.820 8.653 1.346 1.077 µs 6.502 53.23

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 0.036 0.076 0.117 0.451 1.560 5.318 9.893 1.443 5.242 0.895 0.635 ppb 5.6 42.11

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 -97.171 -41.592 -15.622 -2.218 15.895 75.342 204.015 31.517 116.934 17.964 -0.461 µs 4.014 39.66

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 11.771 11.779 11.828 12.128 12.568 12.643 12.649 0.740 0.864 0.227 12.147 ppm 0.3131 2.199
Temp /dev/sda 44.000 44.000 45.000 46.000 48.000 48.000 53.000 3.000 4.000 1.083 46.341 °C
Temp /dev/sdb 54.000 55.000 55.000 57.000 64.000 65.000 66.000 9.000 10.000 2.414 57.183 °C
Temp /dev/sdc 56.000 56.000 56.000 58.000 60.000 60.000 63.000 4.000 4.000 1.502 57.873 °C
Temp /dev/sdd 61.000 61.000 62.000 64.000 72.000 74.000 74.000 10.000 13.000 2.805 64.318 °C
Temp /dev/sde 44.000 44.000 45.000 47.000 49.000 49.000 49.000 4.000 5.000 1.240 47.033 °C
Temp /dev/sdf 55.000 55.000 55.000 58.000 65.000 66.000 66.000 10.000 11.000 2.458 57.909 °C
Temp LM0 28.500 28.500 28.500 30.000 32.250 33.750 42.000 3.750 5.250 1.313 30.177 °C
Temp LM1 39.500 40.000 40.000 41.500 43.500 44.000 47.000 3.500 4.000 1.038 41.556 °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 48.000 0.000 0.000 3.881 0.328 °C
Temp LM12 27.800 44.000 45.000 46.000 48.000 48.000 53.000 3.000 4.000 1.894 46.210 °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 32.500 0.000 0.000 0.128 29.809 °C
Temp LM15 29.750 29.750 29.750 31.250 33.500 35.500 65.000 3.750 5.750 2.496 31.576 °C
Temp LM16 55.000 55.000 55.000 58.000 65.000 66.000 66.000 10.000 11.000 2.473 58.058 °C
Temp LM17 60.000 60.000 60.500 62.000 64.500 66.500 72.000 4.000 6.500 1.380 62.074 °C
Temp LM18 55.000 61.000 62.000 64.000 72.000 74.000 74.000 10.000 13.000 2.885 64.408 °C
Temp LM19 28.000 55.000 55.000 57.000 64.000 65.000 66.000 9.000 10.000 3.386 57.119 °C
Temp LM2 33.000 44.000 45.000 47.000 49.000 49.000 49.000 4.000 5.000 1.660 46.939 °C
Temp LM20 27.000 27.000 28.000 30.000 32.000 38.000 72.000 4.000 11.000 3.027 30.057 °C
Temp LM21 25.000 27.000 27.000 29.000 32.000 36.000 72.000 5.000 9.000 2.810 29.543 °C
Temp LM22 24.000 25.000 25.000 27.000 30.000 34.000 71.000 5.000 9.000 2.951 27.574 °C
Temp LM23 26.000 26.000 27.000 29.000 32.000 38.000 71.000 5.000 12.000 3.048 29.029 °C
Temp LM24 26.000 27.000 27.000 29.000 32.000 36.000 68.000 5.000 9.000 2.588 29.461 °C
Temp LM3 31.500 33.000 33.000 34.000 36.000 36.000 41.000 3.000 3.000 1.019 34.210 °C
Temp LM4 24.000 31.000 31.500 33.000 34.500 35.000 37.000 3.000 4.000 1.277 32.806 °C
Temp LM5 24.000 24.000 24.000 24.000 24.000 24.000 30.500 0.000 0.000 0.432 24.036 °C
Temp LM6 27.000 27.500 28.000 29.000 32.000 60.000 73.000 4.000 32.500 4.039 29.891 °C
Temp LM7 0.000 60.000 60.000 62.000 64.000 66.000 68.000 4.000 6.000 5.361 61.352 °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 30.000 32.000 37.000 73.000 4.000 10.000 3.155 29.879 °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 60.000 60.000 60.500 62.000 64.500 66.500 68.000 4.000 6.500 1.358 62.060 °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) -1,162.516 -99.468 -6.657 65.390 217.631 248.475 1,114.686 224.288 347.943 91.490 77.506 µs -1.98 47.28

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 -1.590 -1.333 -1.051 0.453 0.932 1.081 1.212 1.982 2.414 0.671 0.152 ms -0.6396 2.077

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 -0.143 -0.042 -0.015 0.035 0.073 0.136 11.383 0.088 0.178 0.178 0.038 ms 61.74 3932

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) -97.172 -41.593 -15.623 -2.219 15.896 75.343 204.016 31.519 116.936 17.965 -0.461 µs 4.014 39.66

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) 1.671 4.011 6.120 28.030 85.745 108.786 503.474 79.625 104.775 27.567 35.318 µs 2.541 26.43

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 2.737 4.983 7.439 14.749 32.263 46.702 119.327 24.824 41.719 8.985 16.712 µs 2.929 20.66

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 0.000 0.002 0.003 0.012 0.049 0.071 7.813 0.045 0.069 0.157 0.022 ms 40.27 1785

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) 0.099 0.364 0.562 1.811 6.303 33.764 98.714 5.741 33.400 5.903 2.942 µs 8.402 93.01

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.



Summary


Percentiles...... Ranges...... Skew- Kurt-
Name Min1%5%50%95% 99%Max   90%98%StdDev  MeanUnits nessosis
Local Clock Frequency Offset 11.771 11.779 11.828 12.128 12.568 12.643 12.649 0.740 0.864 0.227 12.147 ppm 0.3131 2.199
Local Clock Time Offset -97.171 -41.592 -15.622 -2.218 15.895 75.342 204.015 31.517 116.934 17.964 -0.461 µs 4.014 39.66
Local RMS Frequency Jitter 0.036 0.076 0.117 0.451 1.560 5.318 9.893 1.443 5.242 0.895 0.635 ppb 5.6 42.11
Local RMS Time Jitter 0.309 0.429 0.520 0.793 2.340 9.082 17.410 1.820 8.653 1.346 1.077 µs 6.502 53.23
Server Jitter 2001:470:e815::8 (spidey.rellim.com) 1.671 4.011 6.120 28.030 85.745 108.786 503.474 79.625 104.775 27.567 35.318 µs 2.541 26.43
Server Jitter 204.17.205.1 2.737 4.983 7.439 14.749 32.263 46.702 119.327 24.824 41.719 8.985 16.712 µs 2.929 20.66
Server Jitter 204.17.205.24 0.000 0.002 0.003 0.012 0.049 0.071 7.813 0.045 0.069 0.157 0.022 ms 40.27 1785
Server Jitter SHM(0) 0.099 0.364 0.562 1.811 6.303 33.764 98.714 5.741 33.400 5.903 2.942 µs 8.402 93.01
Server Offset 2001:470:e815::8 (spidey.rellim.com) -1,162.516 -99.468 -6.657 65.390 217.631 248.475 1,114.686 224.288 347.943 91.490 77.506 µs -1.98 47.28
Server Offset 204.17.205.1 -1.590 -1.333 -1.051 0.453 0.932 1.081 1.212 1.982 2.414 0.671 0.152 ms -0.6396 2.077
Server Offset 204.17.205.24 -0.143 -0.042 -0.015 0.035 0.073 0.136 11.383 0.088 0.178 0.178 0.038 ms 61.74 3932
Server Offset SHM(0) -97.172 -41.593 -15.623 -2.219 15.896 75.343 204.016 31.519 116.936 17.965 -0.461 µs 4.014 39.66
Temp /dev/sda 44.000 44.000 45.000 46.000 48.000 48.000 53.000 3.000 4.000 1.083 46.341 °C
Temp /dev/sdb 54.000 55.000 55.000 57.000 64.000 65.000 66.000 9.000 10.000 2.414 57.183 °C
Temp /dev/sdc 56.000 56.000 56.000 58.000 60.000 60.000 63.000 4.000 4.000 1.502 57.873 °C
Temp /dev/sdd 61.000 61.000 62.000 64.000 72.000 74.000 74.000 10.000 13.000 2.805 64.318 °C
Temp /dev/sde 44.000 44.000 45.000 47.000 49.000 49.000 49.000 4.000 5.000 1.240 47.033 °C
Temp /dev/sdf 55.000 55.000 55.000 58.000 65.000 66.000 66.000 10.000 11.000 2.458 57.909 °C
Temp LM0 28.500 28.500 28.500 30.000 32.250 33.750 42.000 3.750 5.250 1.313 30.177 °C
Temp LM1 39.500 40.000 40.000 41.500 43.500 44.000 47.000 3.500 4.000 1.038 41.556 °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 48.000 0.000 0.000 3.881 0.328 °C
Temp LM12 27.800 44.000 45.000 46.000 48.000 48.000 53.000 3.000 4.000 1.894 46.210 °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 32.500 0.000 0.000 0.128 29.809 °C
Temp LM15 29.750 29.750 29.750 31.250 33.500 35.500 65.000 3.750 5.750 2.496 31.576 °C
Temp LM16 55.000 55.000 55.000 58.000 65.000 66.000 66.000 10.000 11.000 2.473 58.058 °C
Temp LM17 60.000 60.000 60.500 62.000 64.500 66.500 72.000 4.000 6.500 1.380 62.074 °C
Temp LM18 55.000 61.000 62.000 64.000 72.000 74.000 74.000 10.000 13.000 2.885 64.408 °C
Temp LM19 28.000 55.000 55.000 57.000 64.000 65.000 66.000 9.000 10.000 3.386 57.119 °C
Temp LM2 33.000 44.000 45.000 47.000 49.000 49.000 49.000 4.000 5.000 1.660 46.939 °C
Temp LM20 27.000 27.000 28.000 30.000 32.000 38.000 72.000 4.000 11.000 3.027 30.057 °C
Temp LM21 25.000 27.000 27.000 29.000 32.000 36.000 72.000 5.000 9.000 2.810 29.543 °C
Temp LM22 24.000 25.000 25.000 27.000 30.000 34.000 71.000 5.000 9.000 2.951 27.574 °C
Temp LM23 26.000 26.000 27.000 29.000 32.000 38.000 71.000 5.000 12.000 3.048 29.029 °C
Temp LM24 26.000 27.000 27.000 29.000 32.000 36.000 68.000 5.000 9.000 2.588 29.461 °C
Temp LM3 31.500 33.000 33.000 34.000 36.000 36.000 41.000 3.000 3.000 1.019 34.210 °C
Temp LM4 24.000 31.000 31.500 33.000 34.500 35.000 37.000 3.000 4.000 1.277 32.806 °C
Temp LM5 24.000 24.000 24.000 24.000 24.000 24.000 30.500 0.000 0.000 0.432 24.036 °C
Temp LM6 27.000 27.500 28.000 29.000 32.000 60.000 73.000 4.000 32.500 4.039 29.891 °C
Temp LM7 0.000 60.000 60.000 62.000 64.000 66.000 68.000 4.000 6.000 5.361 61.352 °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 30.000 32.000 37.000 73.000 4.000 10.000 3.155 29.879 °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 60.000 60.000 60.500 62.000 64.500 66.500 68.000 4.000 6.500 1.358 62.060 °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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