Infraction: 1. All posters are to make an effort to communicate clearly.
Message to User:
Find your shift key and use it.
hm, i dont know why you want to do the math in your head, it takes way more time and is also more prone to small mistakes. all the formulas are in rawr and as far as i know they do their job very accuratly.
there are may options to adjust the fight conditions, if you walk a lot you can estimate your time walking (thus not dpsing) and set the dps time to 0,9 or something. this indeed might be a bit flawed as is doesnt take into account you can still cast fireblast etc. its impossible to try and find your exact dps for a fight which involves a lot of walking, you'll just have to take a guess, even doing math in your head doesnt solve this.
the slight variations in dps you're talking about looks pretty normal to me, there's always the luck factor a.k.a. crit, and a range of other things that influence your dps and might not be the same every try on a boss.
rawr is there to try to get an as accurate guess of how much dps you'll be putting out with certain gear and buffs. from what i head almost everyone leave the dps time on 1 which is true for only a handfull of fights in the entire game. nevertheless i think rawr is a great tool for comparing gear and finding your best solution.