Your diet and daily activities can vary day to day and over the course of the year.  There are also some things that we eat and do infrequently or seasonally, such as having barbecues and working in the garden in the summer or skiing and shovelling snow in the winter.  By asking you to report what you eat and drink and your activities at different times and in different ways, we can capture various types of information and get a more complete picture of your diet and the activities you engage in. 

Think of it like blood pressure: one reading tells you little, multiple readings show your true pattern.