I am trying to get all of my projects ready for custom Tide Station correction and have run into apparent timestamp discrepancies.

We use a Lowrance HDS-7 and produce files in SL2 format. A sample file is attached. The file was created 2016-07-05 at 4:27 pm local time (EST, UTC - 4 hours) and is only a few data points long. The timestamp on the file and SD card is 8:27 pm (apparently, the correct UTC time). I run RM on a Windows 7 system that displays time in EST.

I have set RM Global Settings: Display: Time to UTC, Import/Export GPS Import to UTC, and made sure Timezone was "UTC" during the Import step. At the time of import, the Source File was displayed with time "2016-07-06T00:27:03", or the file timestamp + 4 hours. After import, the data points all have time stamps like this: "2016-07-06T00:27:15","2016-07-06T00:27:18", etc. So, they appear to have an error of +4 referenced to UTC.

I opened Track Edit and set the Start Time to -4 hours, or 2016-07-05 20:27:03 and closed the Edit window. On reopen, the End Time displays as "7/6/2016 12:27:25 AM", which is in error +4 hours. The timestamps on the data points are unchanged ("2016-07-06T00:27:15" etc.) also in error +4 hours.

I am concerned that, since the End Time is wrong, and the data timestamps are wrong, tide correction will be misapplied. I noticed this problem on real data files, not just the brief one attached. I am looking for any settings or operations I may have missed, or an overall approach that eliminates this issue.

Thank you for your keen attention to support.
Mike

I have the same problem with HDS gen3, I manualy change start time and have no problems with tide correction

There is an issue here where the end time display is not updated when the start time is changed (this is a bug and will be fixed). It shouldn't, however, have any effect on the time offsets, which are calculated as simply the start time + the recorded millisecond time offset. Note that "end time" is a derived value - start time + time offset of the last data point - and has no particular function within RM (it is only displayed for informational purposes in the track properties window). Absolute times for Lowrance log files have always been a bit of an issue (and often unreliable) because they are not recorded anywhere in the file. The only time data present is a time offset from the start of the recording, and the way that we try to determine the start time is by using the last modified time of the file and subtracting the log length. This often (usually) works, but not always, which is why the start time can be edited.
I did look at the data that you posted and couldn't reproduce the issue - when I changed the start time, the track-point times updated as expected. If you can still reproduce this issue, please let me know and I will look into it further.

Our SD card was formatted as FAT32. Once reformatted to NTFS, new sonar files modified timestamp displays in Windows in the correct local time and RM start/end times are correct UTC. I believe this resolves the issue.

Thanks again,
Mike