@ChrisBarker-NOAA As @martinjuckes mentioned in his comment, I'm calling the UTC time 'non-metric' because a time variable for data sampled at a fixed rate based on UTC time stamps converted to elapsed time since an epoch without dealing with leap seconds may contain deviations from what you would expect. If you attempt to 'do math' with the contents, you may find that adding an interval to a time does not produce the time you expected and subtracting two times does not produce the interval expected.
Let's say I have acquired data at regular intervals, **dt**, and I have captured the time by grabbing accurate UTC time stamps for each acquisition. If I construct my time variable by naively converting my acquired time stamps to elapsed time since my epoch UTC time stamp, I might have one or more problems lurking in my time variable. 1. If a leap second occurred over the span of my time variable, there will be a point in the times where one of three problems appear. 1. If **dt** is greater than 1 second, there will be an interval between successive time values that is less than **dt**. The formula **t[i] = t[0] + i*dt** won't hold for all the times in the variable. 1. If **dt** is equal to 1 second, the variable also won't be monotonic. There will be a pair of time values that are identical. 1. If **dt** is less than 1 second, the variable won't be monotonic, but rather than a pair of time values that are identical, there may be a section where one or more time values are less than a preceding value. 1. If one or more leap seconds occurred in the time range between my epoch time stamp and my first acquired time stamp, my time values will be internally consistent, but the whole set of values will be smaller than expected. The non-monotonicity problem is one that I don't even want to get into. And, again, for someone measuring things once an hour (for example) this is all pretty ignorable. -- You are receiving this because you are subscribed to this thread. Reply to this email directly or view it on GitHub: https://github.com/cf-convention/cf-conventions/issues/148#issuecomment-434381038
