alt Hacker NewsA jar of mayonnaise?? you can measure by the spoonful (or better, by weight, since its nutritional value is in the package) whenever you eat.
A month is a long time and the measurement error will accumulate every day, especially with fats. Not so much problem if you do that with cucumber or spinach.
> A month is a long time and the measurement error will accumulate every day, especially with fats
Over several months the errors will average out. Unless you eat out a lot, then the above method doesn't work. However if you are single (this is the most unlikely factor!) and cook most meals at home then calories in the door - what you throw away = calories that you ate. That is good enough.