Custom trend charts

 I am trying to create a simple chart of calories in vs calories out. I add energy and calories burned but in selecting a specific day, the numbers on the graph don't match the numbers on the actual day. I also see a nutrient called 'net Calories' and have no clue what that is. I tried a bit of math between burned and consumed but it doesn't add up. Can someone explain why the graphs don't match the actual day and what Net Calories is? Thx.