Sorry, I was interrupted so didn’t do my normal review of the second paragraph; the issues with using local time.
In theory the uploader software, which runs on a modern computer, can convert local time from the PDM or CGM into UTC, however this relies on the PDM/CGM (the data logger) having records in the same local time as the computer running the upload software. This should normally be the case but if it isn’t the gaps or overlaps will occur. It also seems that both Dexcom Clarity and Glooko display UTC data in the local time of the computer running the web browser, which would lead to the misleading data I describe below when the original data was logged in a different time zone.
Even if the user (me) remembers the rule of setting the PDM clock to the local time of the computer before an upload there is still an issue of what happens to the stored data in the PDM as a result of a time zone change and I can’t see a practical way of avoiding data loss in this case. This is because the only way of handling the time zone change is to change the time of the existing recorded data; so if you skip forward one hour all the prior data also has to be skipped forward. That means that a bolus you did at 9am yesterday will be uploaded as a bolus at 10am yesterday; the alternative would be a gap of one hour which would be just as bad and more difficult to implement.
The issue is that time of day is very important in analyzing the data; so if I’m getting night time lows and day time highs but I spend a week in Dubai (I live in Oregon, USA) the same pattern is going to be presented as night time highs and day time lows when I get back to Oregon and upload the whole package of data from the trip.
The ONLY way round this is to store UTC+time-zone; zulu time (UTC alone) isn’t enough. Indeed the Omnipod PDM uses time-of-day, which is local by definition, to store basal rate programs so using UTC means changing every basal rate program on a local time change!
I was tempted when I started using the G6 to set the receiver to UTC and I could set the PDM to UTC as well because I use a fixed basal these days, however it was obvious that it didn’t really fix the problem because of the importance of time-of-day to the data.
These days I use xDrip+ for data logging of both the G6 and the insulin delivery; I enter boluses manually but lose the temp basals. xDrip+ automatically changes time zones because the Android phone it runs on does. What I don’t know yet (since I haven’t done a TZ change yet) is whether it stores the time zone information, I suspect not.