GMT, BST, DST offsets

[Spoo]

I'm dealing with a bunch of stock market tick data files, one file per
trading day, going from 4-Apr-2008 to present. Each file has around
800,000 records. All timestamps are GMT.

I am trying to adjust GMT to Eastern Time, USA, and further, need to
take into account Daylight Savings Time (DST) vs Standard Time (ST)

Two questions:

1. Does GMT "change"? (ie, does it change by 1 hour for DST vs ST)

2. I understand that British Summertime (BST) changes about a week
differently than DST, but, if GMT is "static" (ie, no changes), then I
probably don't need to worry about BST vs DST, right?

Spoo

[GaryMazzone]

My belief was that GMT never changes.

[Spoo]

I was leaning that way as well, but wasn't sure.

[abhijit]

My belief was that GMT never changes.

That's correct. GMT never changes, but England changes to BST during the course of the summer. GMT is the same as UTC, AFAIK.

[kleinma]

You can probably do this all with .NET timezoneinfo classes.

[Spoo]

You can probably do this all with .NET timezoneinfo classes.

Thanks for idea, but I'm hoping to do this with VB6 and no classes.
I can't imagine that it should be too difficult.

All I need now, I think, is the algorithm for DST and ST.. ie, for 2008 thru
2010, what date it changes fwd and back (I know it's on a Sunday).

2008 >> DST, >> ST
2009 >> DST, >> ST
2010 >> DST, >> ST

[Spoo]

Got this far

      Begin DST     End DST
      ---------     -------
2010  3/14/10       11/7/10 
2009  3/08/09       11/1/09
2008  3/09/08       11/2/08

           GMT - 5           GMT - 4           GMT - 5
        ---------------   ---------------   ---------------
2010    Jan-1 to Mar-14   Mar-14 to Nov-7   Nov-7 to Dec-31
2009    
2008

Need those other dates...

EDIT: Got 'em
Thanks, guys, for info re GMT.

EDIT-2: Even better...
DST beg: 2nd Sunday in Mar
DST end: 1st Sunday in Nov

Spoo