LOL. I'm not going to go back and forth with this. If somebody is using the site for tracking, they will use the site daily to record data. Claiming that "Most people using fitday rarely eat nothing at all for a day" is really not worth my time responding to.
You and I obviously have philosophical differences of opinion here. No problem. Do as you like. But I'm telling you straight that FitDay is not going to take the time to "factor in" missing days because it goes against the goal of the product they are trying to deliver. This of course is my opinion, as well as my opinion that if someone is serious about tracking they will record their calories on a daily basis.
Best wishes with your fitness journey!