Based on data from food nutrition and food composition tables, we know that the calorie content of Ziguangyuan retort cake is 159 calories per 100 grams. The calorie value is calculated based on the composition and partial energy conversion factor of the retort cake. In food nutrition, each food has a specific energy conversion factor. Using the coefficients, the mass of the food is related to its calorie content and the calorie value of the food is known.