<div dir="ltr"><div>The use I have for the data are primarily for accurate display of the sky at any given moment which the post 1970 data does very well. Astronomers avoid using zones generally and use UTC or GMT/LMT for past events but there are some programs such as Starry Night and Skymap (any my software) that use the PC's clock and a zone offset (which can be set to past dates researching such phenomena as the timing and accuracy of occultations with select planetary perturbation terms, etc). Astrologers (not astronomers) have been the primary source for this older information and anyone who wants to display the sky with only the knowledge of what time is on their watch would be interested in this historical data. While the time zone information of the past (particularly the first half of the 20th century) is largely suspect (and really anyone who has done even modest research can tell this), it is important to anyone with this interest. Since the historical data doesn't change much, I maintain a separate database for this info (with warnings) since the tzdb can't promise that it will always be there and many have no interest in this type of use.</div>
<div> </div><div>One might want to keep in mind that there are many who have written access to the tzdb in other languages. Here is one example:</div><div> </div><div><a href="http://code.google.com/p/delphi-tzdb/wiki/TZDBNewsAndUpdates">http://code.google.com/p/delphi-tzdb/wiki/TZDBNewsAndUpdates</a></div>
<div> </div><div>To some extent the historical usage accuracy issue is offset by the fact that the particular use I describe above has worn grooves into the more densely populated areas which has a tendency to be more accurate than outlying areas.</div>
<div> </div></div><div class="gmail_extra"><br><br><div class="gmail_quote">On Wed, Sep 18, 2013 at 8:22 AM, Stephen Colebourne <span dir="ltr"><<a href="mailto:scolebourne@joda.org" target="_blank">scolebourne@joda.org</a>></span> wrote:<br>
<blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div class="im">On 18 September 2013 10:59, Meno Hochschild <<a href="mailto:mhochschild@gmx.de">mhochschild@gmx.de</a>> wrote:<br>
> So I support the removal, since I think the discussed data obviously appear<br>
> to be of very questionable nature. We cannot even consider the discussed<br>
> data as "our best estimate". Of course, there is no 100% guarantee - no<br>
> black and white. If someone can know it better then it is easy to add the<br>
> lost data again. But we should really not let the users in the state of<br>
> wrong assumptions. Stability of data should not be the primary concern,<br>
> rather correctness. And most users (near 100%) don't care about old that is<br>
> to say archeological timezone data.<br>
<br>
</div>Pre-1970 data matters to some more than others. I can see a range of positions:<br>
a) delete all pre-1970 data<br>
b) only have Zones for areas distinct after 1970, other IDs are Links,<br>
full data where available for each Zone<br>
c) only have IDs for areas distinct after 1970, full data where<br>
available for each ID<br>
d) create new IDs where data only differs before 1970<br>
I'm arguing for (c), which I previously believed was the tzdb's goal.<br>
The data deletion is based on (b).<br>
<br>
The quality of data deleted is also of different value to different<br>
people. I'll try to explain it in a different way...<br>
<br>
We know that the quality of the historic data for the Carribean is<br>
dubious. Lets give it an accuracy rating of 20%. One argument is that<br>
removing data with 20% accuracy is a good thing, and that is an<br>
understandable position. However, its important to look at the<br>
consequences of the deletion. Previously, location A (eg. Guadeloupe)<br>
had a 20% accuracy rating for its historic data. After the change it<br>
still has a 20% accuracy rating just with different data. But, that<br>
20% accuracy rating refers to location B (eg. Port of Spain). From the<br>
perspective of location A, the accuracy is now lower, say 5%, because<br>
20% accurate data for location B clearly is even less accurate for<br>
location A.<br>
<br>
I understand that the distinction here is fine. But its rather like<br>
saying "we published a guess 10 years ago for when the first factory<br>
opened in Brussels, but it now OK to replace that data with the guess<br>
we made for when the first factory opened in London" (assuming we<br>
recorded factory opening dates). I value each guess being distinct for<br>
each location in the absence of better information.<br>
<span class="HOEnZb"><font color="#888888"><br>
Stephen<br>
</font></span></blockquote></div><br></div>