Confused about calories?

I'm kind of confused about how the calories portion of this site works. I set my activity level at sedentary, because at the moment I'm working 9-10 hours a day at a desk, most days I try to go on a 2-3 mile walk, but I'm not working out at the gym currently because my husband and I are doing some projects at home after work pretty much every day. So with that setting, it says my daily "burn" is around 1900 calories, but it says I should aim to eat 1700 calories. If I want to lose at least 1 pound per week, shouldn't I create a deficit of 500 calories a day, so I would be eating more like 1400?

If you're walking 2-3 miles every day, I don't think "sedentary" is accurate, no matter how long you're working. I'd go with at least "lightly active."