frankschmitt.org:

40•30•30 is an iPhone app designed to let you quickly and easily calculate the percentage of calories from each of the three major macronutrients based on the number of grams in a serving. 

FAQ

• The application launches and immediately quits!
  Please make sure you are running the latest version of the iPhone operating system. To do this, connect your computer to your iPhone, launch iTunes, and select your iPhone from the devices source list on the left side of the iTunes window. Click the “Check for Update” button and install any available updates. If you still experience problems after updating, try deleting the application from your iPhone and re-installing it.
• The percentages don’t look right!
  This application uses a value of 3.6 calories per gram of carbohydrates, 4.15 calories per gram of protein, and 8.6 calories per gram of fat. These may be slightly different than the values listed on packaging or calculated by the FDA, but this variation is likely less than the that due to the particular mix of proteins, fats, and carbs in a serving. 
• What about fiber?
  Most percentage-based diets don’t count fiber towards the carbohydrates in a serving, because it does not increase blood sugar. However, I decided it would be easier for the user to roll back the carbohydrates dial by the number of grams of fiber than to have the user interface cluttered with another dial. 

If you have any other questions, please feel free to contact me.