We have a web app with scientific timeseries data that we show in graphs and such. The data are measurements from many different sensors, often taken every minute or so.
The timezone the user is currently in may not be the same as the timezone the data is from, both because the user may be elsewhere geographically and because we may be looking at winter data in summer (daylight savings).
Which timezone is it best to use when visualizing the data?
The local timezone of the sensor back when the data was recorded -- this makes most sense when looking back at old data, because then you see high temperatures during the day, etc.
The local timezone of the user, as it was at the time when the data was recorded (use local wintertime for data recorded in winter) -- most people expect times in a web app to reflect their own local time, but this means the data you see depends on where you happen to be right now.
Just show UTC always and let the user deal with it, but most of the time the user will actually be in the same timezone as the sensor, usually not UTC.
There probably isn't a single best answer, is there a common practice?