General Time Issues
As of JTides Version 4.8, some difficult time issues have been addressed for the first ... umm ... time (sorry about that). The first versions of JTides assumed that the real-time tidal display would be viewed on a computer in the same time zone as the tidal reporting station on display. This approach had some obvious limitations.
JTides versions since 4.8 have a somewhat more sophisticated, complex system to deal with time issues. In these versions, the tidal display adopts the time zone and time of day of the reporting station that happens to be on display, using the local system clock and time zone to compute the required differential between zones. What this means is if you have two or more tidal charts available for display in different time zones, the vertical red line meant to represent the present time will always move to the time of day appropriate to the time zone of the tidal site, which is not necessarily the computer's local time. Earlier versions failed to do this and caused a lot of confusion among those who might want an accurate picture of tides at a location not in the local time zone. It remains to be seen whether this new arrangement will also cause confusion.
Second, the time displayed in the status box that appears on the present-time line can show virtually any time zone the user selects. To change time zones, simply press the configuration () dialog button and choose from the "Time Zone" drop-down list. The choices are:
The last option is useful in the case where, for one reason or another, your system's time zone is not correct, or JTides (actually, the Java engine) cannot correctly determine your system's time zone, or you have another reason to choose an arbitrary time zone.
Remember this list of options only affects the time printed in the status box, it never causes the time line to change its position. But please also remember that the time printed in the status box will only agree with the position of the time line if you have chosen "Use Site Time Zone," or your local time zone happens to be the same as the tidal reporting station on display.
System Time Issues
To function correctly, JTides needs to know the date, time of day and time zone where your system is located. There are several reasons this information might not get through:
If Java is not correctly interpreting your chosen time zone, you may have to provide an explicit statement about the time zone in the script you use to launch JTides. Here is an example of a Linux script that launches JTides after establishing a time zone (the complete script lies between the two horizontal lines):
#!/bin/sh export TZ=PST8PDT java -jar JTides.jar
As to the argument of TZ, it can take many forms. Here are the standard forms for typical US time zones:
PST8PDT MST7MDT CST6CDT EST5EDT
But for any arbitrary time zone, you may use a TZ argument of "GMT-8" for US Pacific Time, "GMT-5" for US Eastern time, etc.. Just remember that time zones west of Greenwich are represented by negative numbers, east of Greenwich by positive numbers.