<html><head><meta http-equiv="Content-Type" content="text/html charset=us-ascii"></head><body style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space;" class=""><br class=""><div><blockquote type="cite" class=""><div class="">27. 5. 2020 v 23:39, Bill Gee <<a href="mailto:bgee@campercaver.net" class="">bgee@campercaver.net</a>>:</div><br class="Apple-interchange-newline"><div class=""><div style="white-space: pre-wrap; font-family: monospace; font-size: 15px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; orphans: auto; text-align: start; text-indent: 0px; text-transform: none; widows: auto; word-spacing: 0px; -webkit-text-stroke-width: 0px; margin: 0px;" class="">I am well aware of how Therion processes declination when going through the survey data. I take the trouble to make sure every set of survey data has a date associated with it so that the declinations can be properly calculated.</div><p style="white-space: pre-wrap; font-family: monospace; font-size: 15px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; orphans: auto; text-align: start; text-indent: 0px; text-transform: none; widows: auto; word-spacing: 0px; -webkit-text-stroke-width: 0px; margin: 0px;" class=""> </p><div style="white-space: pre-wrap; font-family: monospace; font-size: 15px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; orphans: auto; text-align: start; text-indent: 0px; text-transform: none; widows: auto; word-spacing: 0px; -webkit-text-stroke-width: 0px; margin: 0px;" class="">As for putting declination on the map ... I have never done that and do not plan to start. I think it is not useful to have it on a map. In 20 years (or whenever) it will be wrong. It is better to just leave it off.</div><br class="Apple-interchange-newline"></div></blockquote></div><br class=""><div class="">Declination up to 1 degree could be not a problem. But there are regions where declination is more than 10 degree. And I know a false theory about development of two huge parallel caves instead of only one system because the author of that theory just omitted inclination of surveys of upper and lower part of that cave from upper and lover entrances (they were not connected). </div><div class=""><br class=""></div><div class="">Softwares for cave data offer the automatic calculation of declination (and grid convergence), so there is not reason not to use it. Therion calculates declination according each day from the model.</div><div class=""><br class=""></div><div class="">Maybe there should be the date when a map was generated under North sign in such case.</div><div class=""><br class=""></div><div class="">Martin</div></body></html>