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
An skimmer calibration automation based on Windows PowerShell can be found here. It scrapes the calibration adjustment from this page and updates two CW Skimmer Server instances and one CWSL_DIGI instance.
225138 RBN spots between 2025-06-17 00:00 and 23:59 UTC. 51115 spots (22.7%) were from reference skimmers (*). Average spot flow was 156 per minute from 195 active CW skimmers. 99307 spots from 183 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 ------------------------------------- 3B8GL -1.5 17 0.999998510 3D2AG +0.4 40 1.000000356 5Z4GO +0.4 17 1.000000419 7N4XCV +0.0 26 1.000000000 AA0O +0.7 101 1.000000706 AC0C-1 -0.1 305 0.999999883 BA4OP +0.0 47 1.000000000 BA6KC +0.1 80 1.000000059 BD7JNA +0.3 41 1.000000251 BG0AJO +0.3 70 1.000000340 BG0AJO/0 +0.1 39 1.000000142 BG2TFW +0.3 81 1.000000264 BG4WOM -0.0 61 1.000000000 BH4RRG +0.0 28 1.000000000 BH4XDZ +0.3 25 1.000000285 BI4MPH-1 +0.0 24 1.000000000 BY4XRA +0.2 43 1.000000166 CT1EYQ* +0.2 919 1.000000235 CX6VM +0.7 45 1.000000740 DE1LON +1.2 1208 1.000001198 DE2SAX +0.6 24 1.000000594 DF2CK +2.1 2516 1.000002090 DF7GB* -0.0 1356 0.999999974 DK0TE +1.1 1286 1.000001139 DK3UA -0.3 478 0.999999661 DK3WW* +0.1 1588 1.000000095 DK9IP* -0.0 727 0.999999989 DK9IP-1* +0.0 940 1.000000010 DL0LA* -0.1 790 0.999999937 DL0PF +10.1 2037 1.000010147 DL1HWS +0.3 1499 1.000000330 DL1HWS-3 +0.5 894 1.000000457 DL1HWS-4 +0.3 149 1.000000332 DL8LAS +0.9 1042 1.000000942 DL8TG* -0.0 1465 0.999999957 DM5GG +0.6 1179 1.000000578 DM6EE +0.1 362 1.000000079 DO4DXA* -0.0 1451 0.999999953 DR4W -1.0 1908 0.999998969 E28AC -1.8 41 0.999998241 EA2CW +0.2 874 1.000000230 EA2RCF-4 -0.0 292 0.999999952 EA5RQ/A +0.4 54 1.000000396 EA5WU* -0.1 1331 0.999999874 ES2RR* -0.1 1485 0.999999947 ES5PC* -0.1 1807 0.999999919 F4GOU +7.7 1468 1.000007742 F4VVG* -0.2 527 0.999999812 F6KGL* +0.1 1288 1.000000129 G0KTN +0.3 1276 1.000000340 G3YPP -0.1 55 0.999999870 G4IRN +0.3 1565 1.000000298 G4ZFE +0.9 1334 1.000000937 GI4DOH-2 +0.1 1271 1.000000140 GX0FRE +0.2 575 1.000000245 HA1VHF +0.7 1530 1.000000732 HA6PX* -0.0 1426 0.999999961 HB9BXE +0.1 1259 1.000000125 HB9DCO -0.6 1104 0.999999389 HG0Y +8.2 349 1.000008150 HG8A +1.6 1517 1.000001567 IK3STG +1.0 1170 1.000000986 IK7YTT* +0.0 2043 1.000000009 IQ9RG* -0.0 1510 0.999999953 IW9GDC +7.6 691 1.000007588 JH7CSU1 +0.7 69 1.000000654 JI1HFJ +0.3 34 1.000000350 JJ2VLY +1.1 86 1.000001078 JN1ILK +0.2 196 1.000000206 K1RA +0.4 530 1.000000352 K2PO/7 +0.7 169 1.000000661 K3PA-1 +0.1 325 1.000000082 K4PP +0.2 204 1.000000209 K5EM +2.1 96 1.000002077 K5TR -5.5 297 0.999994461 K7CO +1.6 119 1.000001579 K7EK +0.8 103 1.000000828 K9IMM -1.3 252 0.999998720 K9LC +0.8 213 1.000000841 KC4YVA +5.6 98 1.000005601 KD2OGR +0.2 174 1.000000205 KD7EFG +0.1 97 1.000000147 KH6LC +0.2 34 1.000000210 KM3T-2 +0.6 306 1.000000582 KM3T-3 -0.0 300 0.999999981 KM3T-5 +0.1 267 1.000000080 KO7SS +1.3 76 1.000001312 KP2RUM -0.1 417 0.999999926 KP3CW +0.4 272 1.000000393 KV4TT -0.4 342 0.999999625 KW7MM +0.6 418 1.000000589 KW7MM/2 -0.3 43 0.999999669 LA6TPA +0.1 350 1.000000054 LA7GIA +0.0 57 1.000000000 LB9KJ* +0.0 313 1.000000000 LZ3CB -0.2 429 0.999999767 LZ4AE +3.4 1162 1.000003353 LZ4UX* +0.1 935 1.000000066 LZ5DI +2.0 1574 1.000001972 LZ7AA +0.8 978 1.000000835 MM0GPZ +0.1 170 1.000000084 MM0ZBH* -0.0 1665 0.999999967 N2CR -0.2 164 0.999999783 N2YCH +10.3 475 1.000010317 N6TV +0.8 122 1.000000818 N9CO +0.1 139 1.000000102 NG7M +0.1 103 1.000000084 NN3RP +0.5 104 1.000000506 NT6Q -0.3 134 0.999999693 NU4F -0.3 296 0.999999661 OE9GHV +0.0 312 1.000000000 OH4KA -0.3 205 0.999999691 OH6BG* +0.1 1599 1.000000125 OK1FCJ* +0.1 1246 1.000000096 ON6ZQ +0.5 898 1.000000462 OZ1AAB +0.3 171 1.000000282 OZ1BZS +0.3 153 1.000000280 OZ4ADX +0.1 211 1.000000135 PA2SQ +0.0 11 1.000000000 PA5KT -0.7 521 0.999999302 PA8MM +0.2 1026 1.000000227 PE5TT +1.1 961 1.000001111 PI4CC +0.2 1720 1.000000150 PR1T -4.5 21 0.999995517 PY2KJ +0.3 12 1.000000297 PY2KNK +2.1 196 1.000002050 R1LB +0.1 259 1.000000121 R4NCU -0.5 109 0.999999542 RK3TD +0.3 153 1.000000264 RK3TD-2 +0.6 46 1.000000601 RU9CZD* -0.1 502 0.999999916 S50U +0.3 540 1.000000254 S53A +0.7 1864 1.000000719 S53F +1.2 55 1.000001237 S53WW +0.7 1443 1.000000653 SE5E +0.3 1863 1.000000290 SM0TCZ +0.0 17 1.000000000 SM1HEV +0.0 299 1.000000025 SM7IUN* -0.2 909 0.999999828 SQ5J +9.5 1379 1.000009489 SZ1A -0.2 1074 0.999999772 TF3Y +1.2 975 1.000001211 TI7W +0.5 631 1.000000491 UA0S +3.7 54 1.000003703 UY2RA -1.2 846 0.999998804 VE3EID -0.8 208 0.999999215 VE6AO -0.6 46 0.999999380 VE6JY +4.6 204 1.000004576 VE6WZ +4.7 79 1.000004726 VE7CC +0.2 46 1.000000215 VK2GEL +0.0 80 1.000000000 VK2RH +0.0 6 1.000000000 VK3RASA -0.8 93 0.999999156 VK6ANC -0.3 36 0.999999725 VU2CPL +0.0 8 1.000000000 VU2PTT +2.9 29 1.000002896 VU2TUM +0.3 62 1.000000319 W1NT-2 +0.0 699 1.000000031 W1NT-6* -0.0 620 0.999999987 W2LB +1.5 46 1.000001547 W2MV +0.8 34 1.000000838 W2NAF +1.1 147 1.000001114 W3OA -7.2 267 0.999992802 W3RGA +0.2 291 1.000000205 W4AX +6.6 13 1.000006581 W4KAZ +0.2 309 1.000000162 W8WTS -0.2 161 0.999999779 W8WWV -1.7 373 0.999998251 WA7LNW +1.1 261 1.000001106 WB6BEE +0.0 27 1.000000000 WC2L +0.7 321 1.000000653 WC8GOP +12.5 16 1.000012467 WE9V +1.3 359 1.000001300 WS2C +6.2 198 1.000006192 WV4P +0.4 183 1.000000428 WX7V/5 +0.0 34 1.000000000 WZ7I +0.7 918 1.000000671 YO2CK +0.3 1089 1.000000286 YO2MAX* +0.0 1412 1.000000040 YO5LD +0.4 570 1.000000400 ZL3X -0.8 200 0.999999188 ZL4YL +2.8 83 1.000002834 ZS1NN -4.9 12 0.999995083 Last updated 2025-06-18 00:15:22 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 0617 0616 0615 0614 0613 0612 0611 0610 0609 0608 --------------------------------------------------------------------- 3B8GL -1.5 -0.1 +0.0 3D2AG +0.4 +0.0 +0.5 +0.0 +0.0 -1.3 +0.2 -0.1 +0.0 +0.0 5Z4GO +0.4 +0.0 +0.6 +0.9 +0.0 +0.4 +0.8 +0.0 +0.4 +0.9 7N4XCV +0.0 +0.0 +1.6 +0.0 +0.4 +0.6 +1.0 AA0O +0.7 +0.6 +0.5 +0.5 +0.4 +0.7 +0.6 +0.7 +0.5 AC0C-1 -0.1 +0.1 +0.1 -0.0 -0.0 -0.0 +0.1 -0.1 -0.1 BA4OP +0.0 +0.0 -0.3 -0.2 +1.0 +0.5 -0.1 +0.0 BA6KC +0.1 +0.0 -0.1 +0.0 -0.1 BD7JNA +0.3 +0.0 +0.1 +0.3 +0.0 +0.0 +0.0 -0.1 BG0AJO/0 +0.1 +0.0 +0.1 +0.0 -0.6 +0.0 +0.0 +0.0 -0.4 BG0AJO +0.3 +0.4 +0.7 +0.6 +0.0 +0.0 +0.1 +0.0 +0.7 +0.5 BG2TFW +0.3 +0.2 +1.0 +0.4 +0.0 +0.8 +0.0 +0.2 +0.5 +0.6 BG4GOV +0.0 +1.9 BG4WOM -0.0 +0.1 +0.1 +0.0 +0.2 +0.3 +0.1 +0.0 +0.1 BH4HKZ -0.6 BH4RRG +0.0 +0.0 +0.7 +0.3 +0.0 +0.0 +0.0 +0.4 +0.4 BH4XDZ +0.3 +0.5 +0.1 -0.1 -0.1 BI4MPH-1 +0.0 +0.0 +0.0 +0.0 +0.3 +0.0 +0.0 BY4XRA +0.2 +0.5 +0.0 +0.5 +0.0 +0.4 +0.0 +0.3 CT1EYQ +0.2 +0.1 -0.1 +0.1 -0.0 -0.1 -0.0 +0.1 +0.5 +0.0 CT7ANO +9.5 +7.6 CX6VM +0.7 +0.4 +0.5 +0.5 +0.3 +0.1 -0.2 +0.2 +0.5 DE1LON +1.2 +1.3 +1.4 +1.8 +1.1 +1.1 +0.9 +0.6 +1.2 +0.9 DE2SAX +0.6 +0.7 DF2CK +2.1 +2.2 +2.2 +2.2 +1.9 +1.7 +1.6 +1.7 +1.5 +1.9 DF7GB -0.0 +0.1 -0.0 -0.0 +0.1 +0.1 -0.0 +0.0 +0.0 -0.0 DG6FL +0.0 +0.0 -0.6 +0.4 DK0TE +1.1 +1.4 +3.9 +3.7 +2.3 +1.8 +1.7 +1.1 +1.6 +1.4 DK3UA -0.3 -0.7 +1.8 +0.0 -0.4 -0.1 -0.4 -0.8 -0.6 -1.1 DK3WW +0.1 +0.2 +0.3 +0.4 +0.2 -0.4 -0.3 -0.3 -0.3 -0.1 DK8NE +0.1 +0.0 +0.7 DK9IP -0.0 +0.0 +0.1 +0.1 -0.2 +0.0 -0.1 -0.0 +0.3 -0.0 DK9IP-1 +0.0 -0.1 +0.0 -0.0 -0.2 -0.1 -0.2 +0.0 +0.1 -0.0 DL0LA -0.1 -0.2 -0.2 -0.1 -0.0 -0.1 -0.3 -0.1 -0.1 -0.2 DL0PF +10.1 +10.1 +9.4 +9.3 +10.3 +9.6 +9.0 +9.5 +9.8 +9.4 DL1HWS +0.3 +0.4 +0.5 +0.5 +0.2 +0.4 +0.4 +0.3 +0.5 +0.5 DL1HWS-3 +0.5 +0.5 +0.8 +0.7 +0.4 +0.6 +0.6 +0.5 +0.5 +0.8 DL1HWS-4 +0.3 +0.5 +0.6 +0.5 +0.7 +0.2 +0.3 +0.2 +0.6 +0.4 DL3OBQ -7.4 -7.1 -7.3 -7.1 -7.6 -7.3 -10.3 DL5RCN +13.0 +13.1 +12.9 DL5RMH -0.3 -0.2 DL8LAS +0.9 +1.0 +1.6 +1.3 +0.6 +0.5 +0.6 +0.5 +0.6 +0.8 DL8LDN +0.0 DL8TG -0.0 +0.1 -0.0 +0.0 -0.0 +0.0 -0.0 -0.0 -0.1 +0.0 DL9GTB +0.5 DM5GG +0.6 +0.5 +0.8 +0.9 +0.8 +3.0 -3.1 -7.4 -5.3 -8.6 DM6EE +0.1 +0.0 +0.1 -0.1 -0.0 -0.0 -0.0 +0.1 +0.1 DM7EE +0.6 DO4DXA -0.0 +0.0 -0.1 -0.0 +0.0 +0.1 -0.1 -0.1 +0.0 +0.0 DR4W -1.0 -0.9 -1.2 -0.7 -0.9 -1.3 -1.1 -1.8 -1.4 -1.3 E28AC -1.8 -0.1 -1.1 -2.2 EA2CW +0.2 +0.3 +0.1 +0.1 +0.5 +0.5 +0.4 +0.4 +0.5 +0.3 EA2RCF-4 -0.0 -0.2 +0.2 +0.4 +1.3 +1.3 +1.4 +0.9 +1.5 +1.3 EA5RQ +0.1 EA5RQ/A +0.4 EA5WU -0.1 -0.2 -0.0 +0.0 +0.1 -0.0 -0.0 -0.0 -0.1 +0.0 ES2RR -0.1 -0.0 +0.0 -0.0 -0.1 -0.1 -0.0 -0.1 -0.1 -0.0 ES5PC -0.1 -0.1 -0.0 -0.0 -0.1 -0.1 -0.0 -0.1 -0.0 -0.0 EU1ST +4.1 +1.4 F4GOU +7.7 +7.6 +8.4 +8.6 +9.2 +8.0 +7.5 +6.6 +6.4 +6.0 F4VVG -0.2 +0.3 -0.0 -0.1 -0.2 -0.3 -0.3 -0.2 F5AHD +0.7 +0.6 +0.7 F6KGL +0.1 +0.1 +0.3 +0.3 +0.1 +0.5 +0.1 G0KTN +0.3 +0.3 +0.4 +0.5 +0.4 +0.3 +0.4 +0.4 +0.4 +0.2 G0TMX -0.6 G3YPP -0.1 +0.3 +0.4 +0.2 +0.6 +0.4 -0.9 +0.5 -0.0 -0.0 G4IRN +0.3 +0.3 +0.8 +0.9 +0.6 +0.6 +0.6 +0.7 +0.8 +0.7 G4ZFE +0.9 +0.8 +0.8 +1.0 +0.5 +0.6 +0.5 +0.5 +0.8 +0.4 GI4DOH-2 +0.1 +0.0 -0.1 +0.1 +0.2 +0.0 +0.1 +0.0 -0.2 -0.0 GX0FRE +0.2 +0.4 +0.8 +0.9 +0.7 +0.5 +0.4 +0.4 +0.4 HA1VHF +0.7 +0.8 +0.9 +0.9 +0.4 +0.6 +0.5 +0.4 +0.7 +0.9 HA2DXC +14.3 HA2NA +0.8 +0.7 +14.4 HA5PP -0.2 -0.3 -0.2 HA6PX -0.0 -0.2 -0.1 -0.0 -0.1 -0.0 -0.1 +0.0 +0.1 -0.0 HA8TKS +0.1 +0.3 HB9BXE +0.1 +0.2 +0.3 +0.3 +0.0 +0.1 -0.0 +0.0 +0.1 +0.1 HB9DCO -0.6 -0.5 -0.2 -0.2 -0.2 -0.8 -0.3 -0.2 -0.5 -0.4 HB9GVO +0.0 +1.1 +1.9 +1.4 HG0Y +8.2 +7.9 +8.1 +8.3 +8.2 +7.7 HG8A +1.6 +1.6 +1.5 +1.6 +1.0 +1.1 +1.4 +1.0 +1.8 +2.4 IK3STG +1.0 +0.7 +1.2 +1.3 +0.6 +0.9 +1.0 +1.1 +1.4 +1.4 IK4VET +4.1 +3.9 +3.5 +1.9 +3.9 +3.5 +3.2 IK7YTT +0.0 -0.0 +0.1 +0.1 -2.9 -6.1 -9.4 -5.5 -6.1 -5.3 IQ9RG -0.0 +0.0 +0.0 +0.1 +0.1 +0.1 +0.1 +0.1 IW9GDC +7.6 +7.5 +7.7 +7.9 +9.0 +8.1 +8.0 +8.1 +8.4 +7.7 JG1DLY +0.0 JH7CSU1 +0.7 +1.4 +1.3 +1.3 +0.9 +1.4 +0.9 +2.0 JI1HFJ +0.3 +1.0 -0.9 +1.3 +0.5 +0.2 -1.8 +0.7 JJ2VLY +1.1 +1.0 +1.0 +0.8 +0.0 +1.4 +0.9 +0.9 +0.6 +1.3 JK1QLQ +0.0 +0.0 +0.8 +0.0 JN1ILK +0.2 +0.3 +0.5 +0.1 +0.0 -0.0 -0.1 +0.1 +0.2 +0.6 K1RA +0.4 +0.4 +0.7 +0.8 +0.9 +0.6 +0.9 +0.6 +0.5 +0.8 K2PO/7 +0.7 +0.4 +0.8 +0.6 +0.4 +0.8 +0.6 +0.7 +0.4 K3PA-1 +0.1 +0.0 +0.0 -0.1 +0.0 +0.2 +0.1 -0.1 +0.1 K3PA-2 -0.6 +0.0 +0.0 K4PP +0.2 +0.3 +0.3 +0.5 +0.2 +0.4 +0.3 +0.1 +0.1 K5EM +2.1 +2.0 +1.5 +1.8 +1.6 +2.5 +3.4 +3.7 +1.6 K5TR -5.5 -4.9 -3.9 -3.6 -12.8 +0.8 +0.7 +1.0 +0.7 K6FOD +0.0 +0.1 +0.6 +0.1 +0.1 +0.2 +0.2 -0.1 K7CO +1.6 +1.0 +1.3 +1.1 +1.1 +1.0 +0.9 +1.0 +0.7 K7EK +0.8 +1.3 +1.6 +3.3 +1.5 +1.3 +0.3 +2.1 +0.8 K9IMM -1.3 -1.2 -1.4 -1.4 +0.0 -0.3 -0.2 -0.1 -0.1 -0.2 K9LC +0.8 +0.8 +0.7 +0.8 +0.8 +0.4 +0.8 +0.5 +0.7 +0.8 KC4YVA +5.6 +6.5 +5.8 +1.0 -3.5 -0.9 -2.1 -2.4 -2.5 KD2OGR +0.2 +0.2 +0.6 +0.2 +1.4 +0.2 +0.4 +0.2 +0.4 +0.1 KD7EFG +0.1 +0.2 +0.5 +0.3 +0.2 +0.3 +0.1 +0.2 +0.4 KH6LC +0.2 +0.0 +0.0 +0.0 +0.3 -0.2 +0.4 +0.3 +0.1 KM3T-2 +0.6 +0.8 +0.4 +0.6 +0.9 KM3T-3 -0.0 -0.1 -0.2 -0.2 +0.0 -0.2 -0.1 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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 KM3T-5 LZ4UX OE9GHV WB6BEE Last updated 2025-06-18 00:15:27 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.