The MenuMaker is helping me think before I eat. But occasionally I'll have an 'off' day when my Protein, Carbs and Fat are totally missing the mark with my PCF. How far can I stray from my PCF before it catches up to me?

The good thing about the PCF approach is that it allows you to achieve your correct PCF values over the day, not just at each meal. However if you blow it big time on one day, then just get back to your correct PCF levels the next day. Generally. If you 'fall off the rails' once very 7-10 days, but get straight back on again, your long term goals won't be too upset.