NTPsec

Pi3/UputronicsV2

Report generated: Thu Jun 22 14:53:44 2017 UTC
Start Time: Thu Jun 15 14:53:02 2017 UTC
End Time: Thu Jun 22 14:53:02 2017 UTC
Report Period: 7.0 days

Daily stats   Weekly stats   24 Hour scatter plot  

Local Clock Time/Frequency Offsets

local offset plot

Percentiles...... Ranges...... Skew- Kurt-
Name Min1%5%50%95% 99%Max   90%95%StdDev  MeanUnits nessosis
Local Clock Time Offset-21.110-1.767-0.811-0.0230.947 1.71015.0041.7583.4770.626-0.000µs-5.116 46.25
Local Clock Frequency Offset-289.902-214.020263.718318.207488.159 561.752610.153224.441775.772112.242320.982ppb 9.353 28.81

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%95%StdDev  MeanUnits nessosis
Local RMS Time Jitter0.0710.1340.1670.6921.208 2.10313.0411.0411.9690.3910.685µs 5.306 43.14

This shows 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%95%StdDev  MeanUnits nessosis
Local RMS Frequency Jitter0.0000.2070.2540.9942.009 3.69241.5031.7553.4850.6981.032ppb 8.903 239.8

This shows 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%95%StdDev  MeanUnits nessosis
Local Clock Offset-21.110-1.767-0.811-0.0230.947 1.71015.0041.7583.4770.626-0.000µs-5.116 46.25

This shows 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 on what temperature sensors you have and 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 the single most important component of frequency drift.

The Local Termperatures 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%95%StdDev  MeanUnits nessosis
Local Clock Frequency Offset-289.902-214.020263.718318.207488.159 561.752610.153224.441775.772112.242320.982ppb 9.353 28.81
Temp ZONE068.75669.83270.90872.52273.060 80.59281.1302.15210.7601.54872.570°C

The frequency offsets and temperatures. Showing frequency offset (red, in parts per million, scale on right) and the temeratures.

These are field 4 (frequency) from the loopstats log file, and field 3 from the temp log .



Local GPS

local gps plot

Percentiles...... Ranges...... Skew- Kurt-
Name Min1%5%50%95% 99%Max   90%95%StdDev  MeanUnits nessosis
nSats1.0006.0008.00013.00017.000 18.00020.0009.00012.0002.85812.431nSat 47.48 193.6
TDOP0.4400.5300.5700.7901.340 2.08099.9900.7701.5501.4360.896 56.42 3681

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. TDOP ranges from 1 to greater than 20. 1 denotes the highest possible confidence level. 2 to 5 is good. Greater than 20 means there will be significant inaccuracy and error.



Peer Offsets

peer offsets plot

This shows the offset of all refclocks, peers 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.



Refclock Offset 127.127.28.0 SHM(0)

peer offset 127.127.28.0 plot

Percentiles...... Ranges...... Skew- Kurt-
Name Min1%5%50%95% 99%Max   90%95%StdDev  MeanUnits nessosis
Refclock Offset 127.127.28.0 SHM(0)-0.049-0.011-0.0050.0000.007 0.0096.7140.0120.0200.0350.001s 186.83.61e+04

This shows the offset of a local refclock in seconds. This is useful to see how the measured offset is behaving.

Closer to 0s is better. An ideal system would be a horizontal line at 0s. Typical 90%% ranges may be: local serial GPS 200 ms; local PPS 20µs.

Clock Offset is field 5 in the peerstats log file.



Refclock Offset 127.127.28.1 SHM(1)

peer offset 127.127.28.1 plot

Percentiles...... Ranges...... Skew- Kurt-
Name Min1%5%50%95% 99%Max   90%95%StdDev  MeanUnits nessosis
Refclock Offset 127.127.28.1 SHM(1)-0.000-0.000-0.000-0.0000.000 0.00013.7480.0000.0000.0250.000s 545.83.001e+05

This shows the offset of a local refclock in seconds. This is useful to see how the measured offset is behaving.

Closer to 0s is better. An ideal system would be a horizontal line at 0s. Typical 90%% ranges may be: local serial GPS 200 ms; local PPS 20µs.

Clock Offset is field 5 in the peerstats log file.



Peer 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%95%StdDev  MeanUnits nessosis
Peer Offset 2001:470:e815::8 (spidey.rellim.com)-167.300-143.937-134.684-110.660-69.853 -54.321106.04264.83189.61620.286-107.209µs-265.9 1775

This shows the offset of a peer or 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 remote. 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 peer 80µs; 90% ranges for WAN servers 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 file.



Peer Offset 204.17.205.1

peer offset 204.17.205.1 plot

Percentiles...... Ranges...... Skew- Kurt-
Name Min1%5%50%95% 99%Max   90%95%StdDev  MeanUnits nessosis
Peer Offset 204.17.205.1-299.14590.037247.287485.739638.732 717.730842.911391.445627.693116.685476.683µs 37.34 138.9

This shows the offset of a peer or 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 remote. 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 peer 80µs; 90% ranges for WAN servers 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 file.



Peer Offset 204.17.205.16

peer offset 204.17.205.16 plot

Percentiles...... Ranges...... Skew- Kurt-
Name Min1%5%50%95% 99%Max   90%95%StdDev  MeanUnits nessosis
Peer Offset 204.17.205.16-1.162-1.100-1.032-0.635-0.184 -0.133-0.0690.8470.9660.270-0.624ms-45.98 185.7

This shows the offset of a peer or 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 remote. 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 peer 80µs; 90% ranges for WAN servers 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 file.



Peer Offset 204.17.205.17

peer offset 204.17.205.17 plot

Percentiles...... Ranges...... Skew- Kurt-
Name Min1%5%50%95% 99%Max   90%95%StdDev  MeanUnits nessosis
Peer Offset 204.17.205.17-69.200-10.470-0.83717.23849.367 63.661242.31150.20474.13114.40517.764µs 2.532 20.98

This shows the offset of a peer or 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 remote. 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 peer 80µs; 90% ranges for WAN servers 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 file.



Peer Offset 204.17.205.23

peer offset 204.17.205.23 plot

Percentiles...... Ranges...... Skew- Kurt-
Name Min1%5%50%95% 99%Max   90%95%StdDev  MeanUnits nessosis
Peer Offset 204.17.205.23-53.053-7.6840.06417.10844.927 62.26198.17044.86369.94512.86017.526µs 2.469 10.71

This shows the offset of a peer or 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 remote. 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 peer 80µs; 90% ranges for WAN servers 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 file.



Peer Offset 204.17.205.27

peer offset 204.17.205.27 plot

Percentiles...... Ranges...... Skew- Kurt-
Name Min1%5%50%95% 99%Max   90%95%StdDev  MeanUnits nessosis
Peer Offset 204.17.205.27-104.712-76.932-26.584-0.4943.163 17.07535.12629.74794.00713.909-3.484ms-9.727 54.03

This shows the offset of a peer or 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 remote. 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 peer 80µs; 90% ranges for WAN servers 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 file.



Peer Offset 204.17.205.30

peer offset 204.17.205.30 plot

Percentiles...... Ranges...... Skew- Kurt-
Name Min1%5%50%95% 99%Max   90%95%StdDev  MeanUnits nessosis
Peer Offset 204.17.205.30-4.605-1.002-0.7350.0240.203 0.5043.7100.9381.5060.336-0.081ms-6.695 35.78

This shows the offset of a peer or 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 remote. 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 peer 80µs; 90% ranges for WAN servers 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 file.



Peer Jitters

peer jitters plot

This shows the RMS Jitter of all refclocks, peers and servers. Jitter is the current estimated dispersion; 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.



Refclock RMS Jitter 127.127.28.0 SHM(0)

peer jitter 127.127.28.0 plot

Percentiles...... Ranges...... Skew- Kurt-
Name Min1%5%50%95% 99%Max   90%95%StdDev  MeanUnits nessosis
Refclock RMS Jitter 127.127.28.0 SHM(0)0.0000.0000.0000.0010.007 0.0106.7140.0060.0100.0560.003s 83.73 8147

This shows the RMS Jitter of a local refclock. Jitter is the current estimated dispersion; 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.



Refclock RMS Jitter 127.127.28.1 SHM(1)

peer jitter 127.127.28.1 plot

Percentiles...... Ranges...... Skew- Kurt-
Name Min1%5%50%95% 99%Max   90%95%StdDev  MeanUnits nessosis
Refclock RMS Jitter 127.127.28.1 SHM(1)0.0000.0950.1360.6081.498 2.39116.3571.3622.2960.5060.682µs 4.728 50.55

This shows the RMS Jitter of a local refclock. Jitter is the current estimated dispersion; 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.



Peer 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%95%StdDev  MeanUnits nessosis
Peer Jitter 2001:470:e815::8 (spidey.rellim.com)0.0000.0060.0080.0220.050 0.068200.3940.0420.0624.3160.128ms 42.46 1974

This shows the RMS Jitter of a remote peer or server. Jitter is the current estimated dispersion; 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.



Peer Jitter 204.17.205.1

peer jitter 204.17.205.1 plot

Percentiles...... Ranges...... Skew- Kurt-
Name Min1%5%50%95% 99%Max   90%95%StdDev  MeanUnits nessosis
Peer Jitter 204.17.205.10.0000.0380.0490.0970.254 0.4286.1020.2040.3900.1810.126ms 15.82 382.2

This shows the RMS Jitter of a remote peer or server. Jitter is the current estimated dispersion; 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.



Peer Jitter 204.17.205.16

peer jitter 204.17.205.16 plot

Percentiles...... Ranges...... Skew- Kurt-
Name Min1%5%50%95% 99%Max   90%95%StdDev  MeanUnits nessosis
Peer Jitter 204.17.205.160.0000.0080.0160.1000.559 0.68867.4850.5430.6801.4300.189ms 42.53 1994

This shows the RMS Jitter of a remote peer or server. Jitter is the current estimated dispersion; 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.



Peer Jitter 204.17.205.17

peer jitter 204.17.205.17 plot

Percentiles...... Ranges...... Skew- Kurt-
Name Min1%5%50%95% 99%Max   90%95%StdDev  MeanUnits nessosis
Peer Jitter 204.17.205.170.0000.0030.0040.0090.037 0.08738.7910.0330.0841.7850.121ms 16.09 335.2

This shows the RMS Jitter of a remote peer or server. Jitter is the current estimated dispersion; 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.



Peer Jitter 204.17.205.23

peer jitter 204.17.205.23 plot

Percentiles...... Ranges...... Skew- Kurt-
Name Min1%5%50%95% 99%Max   90%95%StdDev  MeanUnits nessosis
Peer Jitter 204.17.205.230.0000.0030.0040.0100.034 0.0525.1360.0300.0490.1770.023ms 17.33 413.6

This shows the RMS Jitter of a remote peer or server. Jitter is the current estimated dispersion; 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.



Peer Jitter 204.17.205.27

peer jitter 204.17.205.27 plot

Percentiles...... Ranges...... Skew- Kurt-
Name Min1%5%50%95% 99%Max   90%95%StdDev  MeanUnits nessosis
Peer Jitter 204.17.205.270.0000.0060.0100.1101.998 7.133200.3951.9887.1274.9360.712ms 24.82 914.4

This shows the RMS Jitter of a remote peer or server. Jitter is the current estimated dispersion; 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.



Peer Jitter 204.17.205.30

peer jitter 204.17.205.30 plot

Percentiles...... Ranges...... Skew- Kurt-
Name Min1%5%50%95% 99%Max   90%95%StdDev  MeanUnits nessosis
Peer Jitter 204.17.205.300.0000.0040.0060.0250.326 0.9519.0560.3210.9470.3170.084ms 13.08 313.5

This shows the RMS Jitter of a remote peer or server. Jitter is the current estimated dispersion; 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%95%StdDev  MeanUnits nessosis
Local Clock Frequency Offset-289.902-214.020263.718318.207488.159 561.752610.153224.441775.772112.242320.982ppb 9.353 28.81
Local Clock Time Offset-21.110-1.767-0.811-0.0230.947 1.71015.0041.7583.4770.626-0.000µs-5.116 46.25
Local RMS Frequency Jitter0.0000.2070.2540.9942.009 3.69241.5031.7553.4850.6981.032ppb 8.903 239.8
Local RMS Time Jitter0.0710.1340.1670.6921.208 2.10313.0411.0411.9690.3910.685µs 5.306 43.14
Peer Jitter 2001:470:e815::8 (spidey.rellim.com)0.0000.0060.0080.0220.050 0.068200.3940.0420.0624.3160.128ms 42.46 1974
Peer Jitter 204.17.205.10.0000.0380.0490.0970.254 0.4286.1020.2040.3900.1810.126ms 15.82 382.2
Peer Jitter 204.17.205.160.0000.0080.0160.1000.559 0.68867.4850.5430.6801.4300.189ms 42.53 1994
Peer Jitter 204.17.205.170.0000.0030.0040.0090.037 0.08738.7910.0330.0841.7850.121ms 16.09 335.2
Peer Jitter 204.17.205.230.0000.0030.0040.0100.034 0.0525.1360.0300.0490.1770.023ms 17.33 413.6
Peer Jitter 204.17.205.270.0000.0060.0100.1101.998 7.133200.3951.9887.1274.9360.712ms 24.82 914.4
Peer Jitter 204.17.205.300.0000.0040.0060.0250.326 0.9519.0560.3210.9470.3170.084ms 13.08 313.5
Peer Offset 2001:470:e815::8 (spidey.rellim.com)-167.300-143.937-134.684-110.660-69.853 -54.321106.04264.83189.61620.286-107.209µs-265.9 1775
Peer Offset 204.17.205.1-299.14590.037247.287485.739638.732 717.730842.911391.445627.693116.685476.683µs 37.34 138.9
Peer Offset 204.17.205.16-1.162-1.100-1.032-0.635-0.184 -0.133-0.0690.8470.9660.270-0.624ms-45.98 185.7
Peer Offset 204.17.205.17-69.200-10.470-0.83717.23849.367 63.661242.31150.20474.13114.40517.764µs 2.532 20.98
Peer Offset 204.17.205.23-53.053-7.6840.06417.10844.927 62.26198.17044.86369.94512.86017.526µs 2.469 10.71
Peer Offset 204.17.205.27-104.712-76.932-26.584-0.4943.163 17.07535.12629.74794.00713.909-3.484ms-9.727 54.03
Peer Offset 204.17.205.30-4.605-1.002-0.7350.0240.203 0.5043.7100.9381.5060.336-0.081ms-6.695 35.78
Refclock Offset 127.127.28.0 SHM(0)-0.049-0.011-0.0050.0000.007 0.0096.7140.0120.0200.0350.001s 186.83.61e+04
Refclock Offset 127.127.28.1 SHM(1)-0.000-0.000-0.000-0.0000.000 0.00013.7480.0000.0000.0250.000s 545.83.001e+05
Refclock RMS Jitter 127.127.28.0 SHM(0)0.0000.0000.0000.0010.007 0.0106.7140.0060.0100.0560.003s 83.73 8147
Refclock RMS Jitter 127.127.28.1 SHM(1)0.0000.0950.1360.6081.498 2.39116.3571.3622.2960.5060.682µs 4.728 50.55
TDOP0.4400.5300.5700.7901.340 2.08099.9900.7701.5501.4360.896 56.42 3681
Temp ZONE068.75669.83270.90872.52273.060 80.59281.1302.15210.7601.54872.570°C
nSats1.0006.0008.00013.00017.000 18.00020.0009.00012.0002.85812.431nSat 47.48 193.6
Summary as CSV file


This server:

CPU: Rasberry Pi 3
OS: Gentoo stable
Kernel: 4.4.26, Config
GPS; Uputronics GPS HAT Version 2
GPS/PPS server: gpsd
NTP server: NTPsec
ntp.conf: current

Many thanks to Uputronics for their support and donation of the GPS.

Notes:

20:30 16 Jun 2017 UTC, Change Server/200Hz to Server/500Hz.
21:00 13 Jun 2017 UTC, Change Server/1000Hz to Server/200Hz.
18:00  9 Jun 2017 UTC, Change Server/100Hz to Server/1000Hz.
19:00 21 Dec 2016 UTC SD corruption, start all over again...

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 Peer 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 remote clock 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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