How many calories?

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Ok I have one of those bodymedia things and with my very active job on days i work a fairly busy shift I can burn between 2400-2900. So theoretically I can eat between 1400 and 1900 on those days and have a 1000 calorie deficit. And that day can do ok for a two lb a week loss. But I can not sustain that for more then a few days before I am starving do death and will usually break down and blow my day. So I am trying to keep it more like 750 which is hard still and sometimes it is only about 500. Ok so my question is this. I am 5'5" and 155 so only a little above the overweight range. When I was heavier I could work a long shift and if I didnt go to the gym I could even keep myself down at 1200 calories but I think that actually slowed down my weight loss as those days it would be like a 1300-1500 calorie deficit. But I was ok with that hunger wise. Did I just have more will power? Or is it because I am getting closer to a healthier weight? Should I tone it down a notch? And is 750 deficit ok or should I bring it to 500? my goal is to get down to 130-135 and I know as I get closer I will have to make the deficit smaller and smaller.