search for: tzn

I am analysing some data collected over a number of months from Allentown, PA, which is just north of Philadelphia. I am using as.POSIXct for dates and times, and I need to get the timezone specification correct. Going on the documentation for DateTimeClasses, I believe one way to specify the correct time zone is tz="EST5EDT" I would be grateful for any advice on this. I ask

...TM + 8:00)? I have read in R-help that this is system dependent, but the how to do it still escape. Working with Windows, I have checked the following address given by Gabor Grothendieck in R-help, http://msdn2.microsoft.com/en-us/library/90s5c885.aspx, but I cannot manage with the syntax: *TZ*=tzn[+ | ?]hh[*:*mm[*:*ss] ][dzn]. They mention a three lettre time zone (where can the corresponding codes be found?) to which to add a difference in hours between UTC and the local time... but any trial I did specifying tz="UTM+08" or other combination leads nowhere... Thanks for any hi...