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Time zone reminder for MMW

Home Forums Monitor My Watershed Time zone reminder for MMW

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    • #16712
      Shannon Hicks

      This is just a little reminder that here in North America the local time jumped one hour forward last night for Daylight Saving Time, however the Monitor My Watershed website does not adjust the timestamp for data, meaning everything on the website is still shown in local standard time.

      For example, the MMW webpage from a Mayfly monitoring station today at 13:00 UTC in Pennsylvania in the US Eastern time zone would say “8:00am (UTC-5:00)” when the actual new local time shown on a watch or phone in that area would be 9:00am EDT.  All local times on Monitor My Watershed are shown in Standard Time (EST, CST, PST, etc).  If you viewed a station in California today at that same time, MMW would say “5:00am (UTC-8:00)” while a watch in California at the same time would say 6:00am PDT.

      We frequently get questions from users in the spring and summer asking why all their data appears to be one hour behind, but that’s because the onboard clock on the Mayfly logger board does not adjust itself forward or backward for Daylight Saving Time.  If your station is using one of the recommended logging sketches, the clock chip is actually programmed with the UTC time (Universal Coordinated Time or Greenwich Mean Time) which is a world time standard, and the sketch also has a line that tells the board what the local time zone offset is based on where the station is deployed.  Most of our example sketches have “-5” hours as the offset since we (Stroud Water Research Center) are located in the Eastern time zone.  If you live in another time zone, you’ll want to be sure to change that time zone offset value to match your location, being sure to not apply any Daylight Saving Time or Summer Time offset (depending on your location and time of year).  If you’re unsure of your time zone UTC offset, you can check it on a page like https://www.timeanddate.com/time/zone/usa

    • #16713

      Thanks Shannon. I would not expect the mayfly to adjust for time zone and/or daylight saving time. The logger should record “absolute” time (plus offset), as you described. And that’s what should be recorded in the MMW database. It is then up to the display program, our webpage interface to MMW in this case, to calculate for the users time zone when displaying the time. This is most often accomplished by the display program looking at the client’s settings, such as a PC set to EST with auto adjustment for daylight saving, and adjusting the stored time based on this, and then displaying the appropriate time. There are other benefits to this approach, and it is what I consider to be the “standard” way of handling time storage and display. So … would we consider this a MMW bug that can be reported?

      Thanks again for pointing this out to us. I will pass it on to other mayfly data reviewers who don’t subscribe to this blog.

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