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FAQ: Difference between revisions
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→How does Cumulus handle Daylight Saving Time?
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== How does Cumulus handle Daylight Saving Time? ==
As far as the timestamps in the extreme logs, monthly log, and the graphs, are concerned; Cumulus doesn't do anything in particular for DST.
*It generates timestamps based on the Windows clock.
**So basically, at the start of DST (i.e. when the clocks 'go forward' for the summer) you will get an apparent gap of one hour in your data logs and on graphs.
**Similarly at the end of DST (i.e. when the clocks 'go back' for the winter) you will get an apparent hour of duplicate timestamps in your logs and graphs.
*You will tend to get better results if you leave Cumulus running during the clock change, because if it is stopped you may lose data,
**the exact timing of the affected hours depends on the type of station and the times when Cumulus was running/stopped.
=== ... How do Davis stations handle Daylight Saving Time? ===
Note that there seems to be an issue with Davis stations, either in the console/logger, or in the Davis DLL which Cumulus uses. If you don't have Cumulus running when DST ends, then when you start Cumulus up again, it doesn't receive all of the logger data it needs to catch up to the present time - the previous hour or so is missing. So with Davis stations, I strongly recommend that you leave Cumulus running at the end of DST, if at all possible.▼
Note that there seems to be an issue with Davis stations, either in the console/logger, or in the Davis DLL which Cumulus uses.
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*So with Davis stations, I strongly recommend that you leave Cumulus running at the end of DST, if at all possible.
=== ... How do Fine Offset stations handle Daylight Saving Time? ===
*For Fine Offset stations if you don't have Cumulus running when DST ends in autumn, then when you start Cumulus up again, the catch up ''misses off the first hour after the time Cumulus was stopped'' (unless you have adjusted the time in [[today.ini]] by subtracting one hour for end of DST while Cumulus was stopped).
**This is because the console memory does not time-stamp the data blocks and Cumulus does not remember the console data block used just before shutdown, (after all depending on how long Cumulus has been stopped and the station logging interval, the old memory location could be overwritten by now), but each memory location does contains minutes elapsed since previous memory location used.
**On restart Cumulus just tries to read the appropriate number of hours worth of observations back from the block now marked as latest.
**For example if it was stopped at 2200 DST and restarted at 0600 standard time, Cumulus catches up with the last 8 hours worth of stored measurements as if going back to 2200 standard time, that means it retrieves back to 2300 DST and has forever lost the period 2200 to 2300 DST.
*So with Fine Offset stations, I strongly recommend that you leave Cumulus running at the end of DST, if at all possible.
*At the start of DST in spring, the catch up will ''duplicate the last hour that Cumulus was previously operating'' (unless you have added one hour to the standard time stored in [[today.ini]] for start of DST while Cumulus was stopped).
**e.g. Stopping from 2200 standard time to 0600 DST the catch up goes back to 2200 DST or 2100 standard time.
**Some calculated measurements like average temperature, cooling degree days, and the like will be slightly out, but no measurement is actually lost.
== What formula does Cumulus use for Dew Point? ==
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