Tracking Food Intake and Transitioning to the Next Stage

We have a notebook that lives on our kitchen counter.  It is filled with dates and times and ounces.  We know and have recorded every ounce of formula that LB has eaten ever since he was born. They pretty much make you keep track of feeding times (and dirty diapers) in the hospital and considering we found out about his MCADD on our first night home from the hospital, we never stopped tracking his feedings.  For awhile, we were writing them on a white board in our kitchen, but after a bunch of traveling this summer (sans whiteboard), we shifted to the notebook method. 

At times, I've felt like this is a bit over the top and that maybe we were being too rigid, but we also felt like it was important for us to track his food intake like this so that we could know for certain if he was falling below that "rule of thirds" (where the metabolic specialists say that eating one third less than he normally does in a day could indicate the onset of a problem).  When illness strikes, one quick look at the trusty notebook and it is very easy to tell his specialists that he typically eats 30 ounces per day and today he's only eaten 18, as opposed to wracking our brain and trying to piece it together during an already stressful time. 

Now, I fear that we've become a little too accustomed to it.  With the end of formula and bottles and easily measured food intake on the horizon, losing the notebook method has me a bit apprehensive.  Granted, we do not track his solid food consumption in the notebook, but we still have a sense of his intake for the day by tracking his formula intake.  Without that, will we know when he's not eating enough?  Anyone have any good advice for navigating this transition?