I've also found that using the "browse" foods rather than the "search" feature is more effective. It is a little more intuitive for me. But beware, FitDay uses an average calorie or nutrient value for most foods.
Although a calorie is a calorie, and an Oz is an Oz, the exact nutrient value in the item you have in your kitchen depends on many things, particularly additives in the case of processed food. Calorie values even in non-processed, whole foods can vary somewhat because of biology. Nature doesn't always follow the same recipe when making an apple or a chicken. And things like storage can alter the contents. Slightly freezer burn meats will be a little more concentrated in protein per Oz, because they have dried out, for example.
So, my advise is to think of many calorie values as "plus or minus" a few calories. If you are on a strick calorie regime, intentionally err on the side of caution, because human nature will have us under estimating our consumption.