Cooking fat
Cooking fat is the oil, butter or other fat a food is fried, roasted or dressed in, an ingredient that a plate does not show and that can add a third or more to a dish's calories. IZeat's assistant asks what a dish was cooked or dressed in when the customer's words leave it open, records the fat as its own item with its quantity, and never guesses it from a picture.
A tablespoon of oil is about 115 kcal and about 13 g of fat, and it is invisible on the plate; this is why the cooking question is one of the three the assistant is told to always ask. It asks only when the words leave it open: "grilled chicken, no oil" needs no question, "pan-fried" does. The fat is recorded as an item so the day shows it rather than folding it into the chicken.
The cooking fat is the single largest reason a plate photo cannot give an honest number: the r/loseit test that measured photo estimates against a scale found hidden oil and butter among the biggest errors. IZeat's rule of questions before numbers exists for this item more than any other, and a customer who answers it once learns to say it unprompted.
Put it into practice: Logging a meal.
Updated