GMT, BST, DST offsets

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

My belief was that GMT never changes.

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

Quote:

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Originally Posted by GaryMazzone

My belief was that GMT never changes.

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

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

Quote:

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Originally Posted by kleinma

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

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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

Got this far

Code:

---

      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