Skimmer frequency accuracy
To be a good RBN citizen a skimmer should have a frequency accuracy of 2ppm or better.
VERY IMPORTANT: To use the data below to improve the accuracy of your skimmer, multiply the current value of FreqCalibration in your skimmer software’s settings file with the suggested adjustment factor listed below.
The location of the settings files are:
CW Skimmer Server: %appdata%\Afreet\Products\SkimSrv\SkimSrv.ini
CW Skimmer: %appdata%\Afreet\Products\CwSkimmer\CwSkimmer.ini
The data listed below is based on yesterday’s RBN data, 00:00 to 23:59 UTC. This means that when making adjustments, changes in calibration will typically not have full impact on the listed data until the second day after the change.
The deviation estimates are based on spots on all active bands (40m and higher) from the respective skimmer. If different hardware is used for the different bands, the deviation number may thus not represent the actual deviation for a particular band. It is a good practice to run a separate instance of RBN Aggregator with a unique SSID for each hardware, (SM7IUN-1, SM7IUN-2, etc.)
A link to the software used to produce the tables can be found at the bottom of this page. It runs as a cron job in an Ubuntu container on my Synology server and uploads to this WordPress website shortly after midnight UTC daily.
The deviation estimation is done in two steps. The first step uses a small number of highly accurate skimmers (called “anchors” in the code, typically GPSDO-controlled skimmers) as reference. The whole estimation process is then repeated one more time but using both the anchors as well as all skimmers determined to be the “good” as reference. The “good” skimmers are those with less than 0.15ppm average deviation from the anchors, producing more than 100 qualifying spots (the qualification criteria of spots are outlined below.)
Repeating the analysis with this this extended set of skimmers as frequency references drastically increases the geographical coverage of the analysis thereby increasing the number of qualifying spots which means a much more reliable deviation estimates for all skimmers. The skimmers used as reference skimmers in the second stage (i.e. both anchors and “good”) are marked with an asterisk in the table below.
When looking at the numbers, keep in mind that the deviations estimated by the algorithm are 100 to 1000 times smaller than the 100Hz resolution of RBN frequency data. The input data is thus extremely “noisy” which inevitably leads to statistical variations. This is also the reason for not including spots under a certain frequency. Doing so would skew the statistics and cause underestimation of the frequency error.
Due to propagation characteristics, operator behavior (e.g. small QSY), and just statistical variations due to the 100Hz rounding, some skimmers selected as reference skimmers in the first stage may have more than 0.2ppm deviation in the second stage. This is not an error.
If you do not see your skimmer in the list below in spite of it successfully feeding spots to RBN the most likely reason is that it is off in frequency. The analytics discards all spots from skimmers having more than 0.5kHz frequency error.
if you want to implement an automated calibration of your skimmer you can access the skew data in machine-readable CSV format here https://sm7iun.se/rbnskew.csv
460036 RBN spots between 2024-12-04 00:00 and 23:59 UTC. 123704 spots (26.9%) were from reference skimmers (*). Average spot flow was 319 per minute from 194 active CW skimmers. 224810 spots from 187 skimmers qualified for analysis by meeting the following criteria: * Mode of spot is CW. * Also spotted by a reference skimmer within 1000 spots. * Also spotted by a reference skimmer within 10s. * SNR is 3dB or higher. * Frequency is 7000kHz or higher. * Frequency deviation from reference skimmer is 0.5kHz or less. * At least 5 spots from same skimmer in data set. Skimmer [ppm] Spots Adjustment ------------------------------------- 2E0INH* +0.1 1404 1.000000051 3B8CW +0.2 229 1.000000156 3D2AG +0.9 293 1.000000937 5Z4GO +0.4 20 1.000000356 AA0O +0.3 348 1.000000302 AC0C-1 -0.5 3215 0.999999499 BA6KC +0.1 152 1.000000140 BD8CS +0.2 75 1.000000190 BG0AJO -0.2 68 0.999999790 BG2TFW +7.9 146 1.000007931 BG4GOV +0.4 67 1.000000425 BH4RRG +0.2 90 1.000000159 BH4XDZ -0.3 56 0.999999745 BI4MPH-1 -0.5 39 0.999999452 BY4XRA +0.2 84 1.000000170 CT1EYQ -0.4 1255 0.999999566 DC8YZ* +0.1 2722 1.000000067 DE1LON +0.7 1964 1.000000741 DF2CK -0.2 3767 0.999999833 DF7GB* -0.1 1902 0.999999928 DJ1RK +0.1 984 1.000000094 DK0TE +0.3 1930 1.000000256 DK3UA -7.4 764 0.999992595 DK9IP -0.4 1480 0.999999552 DK9IP-1* -0.1 1896 0.999999878 DL0LA -0.3 1217 0.999999651 DL1HWS* -0.0 2156 0.999999956 DL1HWS-3 +0.2 986 1.000000234 DL5RCN +4.9 306 1.000004899 DL8LAS -3.1 5397 0.999996927 DL8TG* +0.0 1658 1.000000030 DL9GTB +0.6 336 1.000000574 DM5GG -13.6 128 0.999986362 DM6EE* +0.0 1871 1.000000040 DR4W -3.9 2351 0.999996129 EA1RX -0.8 77 0.999999198 EA1URA -0.5 1762 0.999999489 EA2CW -0.3 1987 0.999999667 EA2RCF-4* -0.0 1302 0.999999971 EA5RQ +0.4 429 1.000000382 EA5RQ/A +0.0 76 1.000000000 EA5WU* +0.0 2281 1.000000005 ES2RR* +0.1 1736 1.000000064 ES5PC* -0.0 2087 0.999999959 F4GOU +3.8 1860 1.000003769 F4VVG* +0.0 1116 1.000000029 F6IIT -0.9 2577 0.999999116 F6KGL +0.2 2134 1.000000153 G0KTN* -0.0 1986 0.999999973 G3XBI +0.2 1119 1.000000210 G3YPP +0.0 209 1.000000000 G4AON +0.9 180 1.000000946 G4FRE +1.2 659 1.000001181 G4IRN +0.3 2619 1.000000316 G4ZFE +0.3 2540 1.000000273 GI4DOH +0.1 1296 1.000000150 HA1VHF -0.0 261 0.999999997 HA6PX* +0.0 2054 1.000000031 HA8TKS* +0.2 1590 1.000000167 HB9BXE* +0.0 1787 1.000000030 HB9DCO -0.4 1506 0.999999601 HG0Y +6.3 124 1.000006265 HG8A +0.4 2245 1.000000428 IK3STG +3.2 1324 1.000003159 IK4VET +0.5 2393 1.000000527 IZ2CPS -0.9 23 0.999999105 JH7CSU1 +1.0 202 1.000000959 JI1HFJ -5.8 25 0.999994156 JJ2VLY -0.9 32 0.999999073 JN1ILK -0.4 459 0.999999601 K1RA -0.4 2138 0.999999597 K2PO/7 -5.9 1054 0.999994113 K3LR +0.2 1069 1.000000182 K3PA-1* +0.0 1524 1.000000009 K3PA-2 -1.6 329 0.999998393 K4PP -0.4 1423 0.999999576 K5EM +0.1 1015 1.000000148 K5TR +0.2 636 1.000000235 K6FOD* +0.0 741 1.000000045 K7CO +0.3 1110 1.000000330 K7EK -0.0 392 0.999999982 K9IMM* -0.1 1752 0.999999909 K9LC* +0.0 2126 1.000000041 K9QC +0.5 300 1.000000503 KA7OEI +0.1 202 1.000000108 KD2OGR +0.4 1073 1.000000390 KH6LC +0.3 222 1.000000278 KM3T-2* -0.2 989 0.999999780 KM3T-3 +0.3 2251 1.000000292 KO7SS -0.1 977 0.999999908 KV4TT -0.2 1577 0.999999797 LA6TPA -6.7 1033 0.999993268 LB9KJ* -0.1 665 0.999999939 LZ3CB* -0.0 1202 0.999999971 LZ4AE -0.2 2232 0.999999796 LZ4UX* +0.0 1510 1.000000005 LZ5DI -0.2 1926 0.999999837 MM0ZBH +0.3 2714 1.000000296 N6TV +0.5 420 1.000000461 N7TUG +15.5 138 1.000015493 N8DXE +1.5 795 1.000001486 N9CO* -0.0 1984 0.999999977 ND7K -1.1 1427 0.999998887 NG7M* +0.1 914 1.000000125 NN3RP* -0.5 730 0.999999499 NT6Q +0.6 897 1.000000561 NU4F* -0.0 1513 0.999999952 OE6TZE* +0.0 1583 1.000000027 OE9GHV* -0.0 2540 0.999999986 OH4KA -2.6 1809 0.999997399 OH6BG* -0.0 1652 0.999999987 OK1FCJ +0.1 2169 1.000000136 OK1HRA -3.6 2041 0.999996411 OK4QRO +1.6 1612 1.000001605 OK4ZAW* +0.0 719 1.000000019 ON4EM +1.4 21 1.000001356 ON6ZQ -0.4 1646 0.999999599 OZ1AAB +0.2 772 1.000000193 OZ1BZS +0.6 511 1.000000594 OZ4ADX +0.8 241 1.000000761 PA0MBO +0.6 305 1.000000630 PA1T +0.2 1858 1.000000215 PA3GRM +0.0 6 1.000000000 PA8MM -0.7 1248 0.999999274 PE5TT +0.4 1662 1.000000357 PI4CC* +0.0 2287 1.000000013 R6YY +0.1 248 1.000000057 RK3TD +0.9 1934 1.000000853 RN4WA +1.1 1625 1.000001087 RU9CZD -5.7 1125 0.999994338 S50ARX* -0.1 2046 0.999999882 S50U* -0.2 1106 0.999999784 S53A +0.4 1818 1.000000372 S53WW -1.2 2154 0.999998778 SE5E -0.3 2501 0.999999665 SM0TCZ +2.0 209 1.000002002 SM7IUN* +0.1 1677 1.000000058 SQ5J +6.7 1784 1.000006695 SQ5OUO +6.7 116 1.000006750 SV1CDN +5.4 16 1.000005353 SZ1A +0.2 1827 1.000000174 TF3Y +1.2 6 1.000001189 TI7W +0.3 1477 1.000000300 UA0S -0.6 763 0.999999447 UA4CC +12.9 270 1.000012858 UD4FD* -0.1 514 0.999999926 V51YJ +1.5 65 1.000001517 VE3EID* +0.1 2282 1.000000114 VE6AO -1.5 787 0.999998507 VE6JY +3.0 1433 1.000003014 VE6WZ +4.7 1207 1.000004736 VE7CC +1.0 550 1.000000996 VK2GEL +1.5 384 1.000001526 VK2RH -0.7 81 0.999999340 VK3RASA -0.3 132 0.999999676 VK6ANC -1.5 158 0.999998529 VR2FUN-77 -0.3 841 0.999999708 VU2CPL +0.0 8 1.000000000 VU2PTT -0.2 122 0.999999825 W1NT-2* +0.1 2197 1.000000095 W1NT-6* +0.0 2864 1.000000034 W2LB +0.9 312 1.000000865 W2MV +0.2 402 1.000000177 W2NAF +1.3 1563 1.000001345 W3DAN +1.4 813 1.000001400 W3LPL -2.9 563 0.999997130 W3OA* +0.0 2128 1.000000044 W3RGA -0.3 2153 0.999999744 W4AX +5.1 237 1.000005101 W6YX -0.1 1457 0.999999880 W8WTS -0.5 1704 0.999999477 W8WWV -2.0 1926 0.999998026 WA7LNW +0.2 1613 1.000000192 WB6BEE +0.0 1882 1.000000045 WC2L -0.3 1833 0.999999727 WC8GOP +6.6 132 1.000006648 WE9V* -0.2 2017 0.999999827 WS2C +4.2 1734 1.000004217 WS3W +3.5 772 1.000003532 WV4P* +0.0 1311 1.000000035 WZ7I* +0.1 2601 1.000000078 YO2CK -0.3 2235 0.999999708 YO2MAX +0.1 2244 1.000000145 ZF1A +7.7 822 1.000007720 ZF9CW -0.3 2379 0.999999681 ZL3X +1.1 477 1.000001064 ZS1NN -3.7 67 0.999996322 Last updated 2024-12-05 00:15:42 UTC
Historical skimmer frequency accuracy
Below you will find historical accuracy data for the past ten days. Do not be concerned over minor daily variations. Since RBN spots only have 100Hz frequency accuracy, the input data is very noisy. Even for a perfectly accurate skimmer, the typical RMS rounding error across all shortwave bands is around 3ppm. This means that for a skimmer with 1000 spots per day the statistical variation is up to 0.2ppm. For skimmers with less than 100 spots per day the statistical variation can be above 2ppm. The content of the table below is based on the historical content of the above table.
Skimmer 1204 1203 1202 1201 1130 1129 1128 1127 1126 1125 --------------------------------------------------------------------- 2E0INH +0.1 +0.0 +0.0 +0.1 +0.1 +0.1 +0.1 +0.2 +0.0 +0.0 3B8CW +0.2 +0.1 +0.2 +0.2 +0.3 +0.3 +0.2 +0.3 +0.2 +0.2 3D2AG +0.9 +0.6 +0.1 +0.4 +0.4 +0.3 +0.1 +0.1 +0.0 -0.0 3V8SS -1.6 -2.4 -2.3 -2.1 -2.1 +0.5 +0.4 5Z4GO +0.4 +0.3 -0.7 +0.6 +0.4 +1.6 +1.5 +0.9 +1.3 AA0O +0.3 +0.1 +0.4 +0.3 +0.2 +0.2 +0.3 +0.3 +0.2 +0.4 AC0C-1 -0.5 -0.0 -0.3 -0.2 -0.1 +0.0 -0.3 -0.2 +0.0 +0.1 BA6KC +0.1 +0.0 -0.0 +0.1 +0.0 +0.1 +0.0 -0.3 -0.2 +0.0 BD7JNA +0.0 -0.0 BD8CS +0.2 -0.1 +0.0 -0.0 +0.0 BG0AJO -0.2 +0.0 -0.3 +0.1 +0.0 -0.4 +1.1 -0.1 +0.0 +0.0 BG0BPZ +0.1 BG2TFW +7.9 -12.2 -11.9 -8.0 -8.7 -9.8 BG4GOV +0.4 +0.2 +0.1 +0.2 +0.3 -0.8 +0.0 +0.3 BH4RRG +0.2 +0.0 -0.2 +0.1 +0.1 +0.0 +0.1 +0.0 +0.0 +0.0 BH4XDZ -0.3 +0.0 +0.0 -0.0 -0.0 +0.0 +0.0 +0.2 +0.0 +0.0 BI4MPH-1 -0.5 +0.1 +0.1 +0.1 +0.1 +0.0 +0.2 -0.2 +0.0 +0.0 BY4XRA +0.2 +0.0 +0.1 +0.3 -0.1 +0.0 +0.4 +0.2 -0.2 +0.0 CT1EYQ -0.4 -0.4 -0.2 -0.2 -0.2 -0.0 -0.6 -0.9 -0.8 -0.4 CT7ANO +5.4 DC8YZ +0.1 +0.1 +0.1 +0.1 +0.1 +0.1 +0.0 +0.1 +0.0 +0.1 DE1LON +0.7 +1.5 +0.8 +0.2 +0.3 -0.3 -0.4 -0.6 -0.7 -0.6 DF2CK -0.2 -0.1 -0.3 -0.3 -0.2 +0.0 +0.1 -0.1 -0.0 -0.0 DF2CK-1 +0.0 -1.5 -1.6 -0.5 DF7GB -0.1 -0.0 -0.0 +0.1 -0.0 -0.0 +0.1 +0.1 -0.1 -0.0 DJ1RK +0.1 +0.1 -0.0 -0.1 +0.1 +0.1 +0.2 +0.3 +0.2 +0.3 DK0TE +0.3 +0.1 +0.1 +0.1 +0.2 +0.2 +0.1 +0.4 +0.3 +0.4 DK1MAX -0.1 +0.0 -0.0 -0.1 DK3UA -7.4 -5.8 -7.9 -6.4 -11.2 -6.6 -7.9 DK8NE -1.6 DK9IP -0.4 -0.4 -0.5 -0.5 -0.6 -0.5 -0.4 -0.5 -0.6 -0.4 DK9IP-1 -0.1 -0.2 -0.0 -0.1 -0.2 -0.1 -0.1 -0.2 -0.1 -0.1 DL0LA -0.3 -0.1 -0.3 -0.3 -0.3 -0.3 -0.3 -0.4 -0.2 -0.2 DL1HWS -0.0 -0.0 -0.0 -0.1 -0.1 -0.1 -0.1 -0.1 -0.0 -0.0 DL1HWS-3 +0.2 +0.1 +0.2 +0.2 +0.3 +0.2 +0.1 +0.2 +0.1 +0.1 DL3OBQ +32.2 +22.2 DL5RCN +4.9 +12.0 +11.6 +11.3 +9.7 +12.2 DL8LAS -3.1 -3.4 -3.0 -3.0 -2.9 -2.8 -2.8 -2.8 -1.4 +0.2 DL8TG +0.0 +0.0 -0.1 -0.1 -0.0 +0.0 -0.1 -0.1 -0.0 -0.0 DL9GTB +0.6 +0.2 +0.5 +0.4 +1.0 +0.7 +0.7 +0.6 +0.5 +0.1 DM5GG -13.6 -1.1 -0.2 -0.0 +0.5 +0.4 +0.2 -0.1 +0.2 +0.4 DM6EE +0.0 +0.1 -0.1 +0.0 -0.0 -0.0 -0.2 +0.0 -0.1 +0.0 DP7D +5.2 -9.8 +10.5 +11.6 +11.2 +11.7 +12.6 DR4W -3.9 -3.9 -4.1 -4.3 -4.3 -3.4 -3.2 -3.5 -3.0 -3.0 EA1RX -0.8 -0.6 -0.4 -1.8 -0.9 -2.0 -0.2 -1.3 EA1URA -0.5 -0.5 -0.5 -0.1 -0.2 -0.1 -0.3 -0.3 -0.5 -0.2 EA2CW -0.3 -0.2 -0.1 -0.1 -0.2 -0.2 -0.3 -0.3 -0.3 -0.1 EA2RCF-4 -0.0 -0.1 -0.2 -0.1 -0.2 -0.1 -0.2 -0.3 -0.4 -0.2 EA5RQ +0.4 +0.3 +0.3 +0.2 +0.2 +0.5 +0.2 +0.3 +0.3 +0.5 EA5RQ/A +0.0 +0.0 +0.0 +0.1 +0.0 -0.0 +0.0 +0.6 EA5WU +0.0 +0.0 +0.0 -0.0 -0.0 +0.1 -0.0 -0.0 -0.1 +0.1 ES2RR +0.1 -0.1 -0.1 -0.1 -0.0 +0.0 -0.1 -0.1 -0.0 -0.1 ES5PC -0.0 -0.1 -0.1 +0.0 -0.0 +0.0 +0.0 -1.1 -2.9 F4EGZ +1.5 F4GOU +3.8 +4.1 +4.0 +4.1 +4.6 +4.4 +3.9 +4.2 +3.6 +4.3 F4VVG +0.0 -0.1 +0.0 -0.1 -0.1 +0.0 -0.1 -0.2 +0.0 -0.2 F5AHD +0.5 F6IIT -0.9 -0.5 -0.5 -0.9 -1.1 -0.5 -0.5 -0.6 -0.6 -0.3 F6KGL +0.2 +0.2 +0.2 +0.2 +0.2 +0.1 +0.0 +0.1 +0.1 +0.2 F8DGY -1.1 -1.3 -1.8 -1.0 -0.6 -0.8 -0.8 -0.9 F8UKP -1.5 -1.5 -2.3 -1.5 -1.7 -1.7 -1.9 G0KTN -0.0 +0.1 +0.1 +0.1 +0.1 -0.0 -0.1 +0.0 +0.1 +0.1 G0TMX +0.1 +0.1 G3BJ +0.2 +0.8 +0.3 G3XBI +0.2 +0.2 +0.3 +0.3 +0.2 G3YPP +0.0 -0.1 -0.3 +0.1 +0.0 -0.0 +0.0 -0.1 -0.0 -0.1 G4AON +0.9 +0.7 +1.0 +0.8 G4FRE +1.2 +1.1 +1.4 +1.3 +1.5 +1.3 +1.2 +1.0 +1.0 G4HSO -0.4 +0.3 +0.4 +0.2 -0.2 -0.5 -0.0 G4IRN +0.3 +0.1 +0.2 +0.4 +0.4 +0.2 +0.0 +0.3 +0.1 +0.2 G4ZFE +0.3 +0.2 +0.2 +0.2 +0.2 +0.3 +0.0 +0.3 +0.2 +0.4 G4ZFE-1 +0.0 GI4DOH +0.1 -0.0 +0.1 +0.2 +0.2 +0.2 -0.1 -0.0 +0.0 +0.2 GSWL1 +1.3 +0.0 HA1VHF -0.0 +0.1 +0.2 +0.2 +0.4 +0.4 +0.4 -1.9 -3.0 -2.6 HA5PP +0.3 HA6PX +0.0 -0.0 -0.1 -0.1 -0.0 +0.1 +0.0 -0.1 -0.0 -0.0 HA8TKS +0.2 +0.1 +0.1 +0.2 +0.2 +0.2 +0.1 +0.1 +0.1 +0.1 HB9BXE +0.0 +0.1 +0.0 -0.3 -0.1 +0.1 +0.1 +0.1 +0.1 +0.2 HB9DCO -0.4 -0.3 -0.4 -0.4 -0.5 -0.2 -0.4 -0.3 -0.5 -0.5 HG0Y +6.3 +5.8 +6.5 +6.1 +6.1 +6.7 +6.5 +6.3 +6.5 +6.3 HG8A +0.4 -0.6 +0.1 -1.4 -1.1 -0.1 +0.0 -0.2 +0.3 +0.3 IK3STG +3.2 +3.5 +3.1 +3.2 +3.5 +2.9 +2.9 +3.5 +4.0 IK4VET +0.5 +0.5 +0.7 +0.6 +0.9 +0.8 +1.0 +0.8 +0.6 +0.7 IZ2CPS -0.9 -0.3 -0.7 -5.7 -4.7 -4.1 JG1DLY -0.3 -0.4 +0.0 JH7CSU1 +1.0 +1.3 +1.9 +1.9 +1.7 +1.1 +1.6 +1.5 +2.4 +1.5 JI1HFJ -5.8 -1.9 -1.9 -5.3 -2.3 -1.2 -2.2 -5.5 -0.6 -2.5 JJ2VLY -0.9 -1.8 -1.2 +1.3 +1.4 -0.9 +0.1 +0.0 -0.1 +1.2 JK1QLQ +0.1 -0.3 +0.0 +0.6 +0.0 +0.2 +0.0 JN1ILK -0.4 -0.2 -0.2 -0.3 -1.2 -1.1 -0.2 -0.5 -0.2 -1.6 K1RA -0.4 -0.3 -0.6 -1.0 -1.2 -0.6 -0.3 -0.1 -0.0 -0.2 K2PO/7 -5.9 -7.1 -4.0 +0.2 +0.3 +0.5 K3LR +0.2 +0.4 +0.3 +1.0 +1.1 +0.2 -0.2 +0.2 +0.3 +0.1 K3PA-1 +0.0 -0.0 +0.0 -0.0 -0.0 -0.0 +0.0 -0.0 -0.0 -0.1 K3PA-2 -1.6 -1.4 -0.9 -1.3 -1.2 -1.9 -2.2 -1.6 -1.6 -1.5 K4PP -0.4 -0.1 -0.2 -0.1 -0.0 +0.0 -0.1 -0.2 +0.1 +0.1 K5EM +0.1 +0.1 -0.0 +0.2 -0.2 -0.1 +0.0 +0.1 -0.1 +0.1 K5TR +0.2 +0.1 +0.1 -0.0 -0.1 K6FOD +0.0 -0.0 -0.0 +0.1 +0.1 +0.0 +0.1 +0.1 +0.1 -0.0 K7CO +0.3 +0.2 +0.1 +0.1 +0.1 +0.1 +0.0 +0.1 +0.1 +0.1 K7EK -0.0 -0.0 +0.1 +0.0 +0.1 +0.1 -0.0 -0.1 +0.1 K9IMM -0.1 -0.1 -0.1 -0.1 +0.0 -0.0 -0.2 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-3.8 -3.3 -3.1 -3.9 -3.3 -4.6 -3.9 -3.4 Last updated 2024-12-05 00:15:52 UTC
Anchor skimmers
The below skimmers use external frequency references and are confirmed to have continuous, high accuracy. Their accuracy is also confirmed against each other on a daily basis.
DF7GB ES2RR LZ3CB LZ4UX OE9GHV WB6BEE Last updated 2024-12-05 00:15:52 UTC
It is the owners of these skimmers who make this web page possible. Thank you.
To get good geographic coverage and a good size dataset, a two-step method is used for the analysis shown above. Since the second step also relies on spots from skimmers with slightly lower accuracy the displayed error for the anchor skimmers may not always be 0.0, even though they are perfectly accurate.
Software
The software powering this page can be found on github.