the use of timezone names like "EST" and "PST" is really not a good idea because these can have different meanings throughout the world. These are really only meaningful when used internally within a specific country or region.
Which is the purpose of the offset figure—to eliminate any ambiguity. Determining the local time-zone name is a simple matter of asking the OS for it—which is possible under Windows, at least for the current day. (Windows is not equipped to provide reliable time-zone info, for days outside of the observance of the current rules (e.g. before the recent DST threshhold changes in the US); but that's another issue.)
