From 1989 the National Readership Survey in Denmark is conducted by using the FRY-method and the CATI-technique. The reading probabilities are a very essential part in the FRY-model. The paper describes how they are calculated and how they are corrected if they are illogical. The questions used for calculation of the reading probabilities are the frequency-question and the FRY-question. As the number of FRY-readers are of decisive importance for the statistical margins of the coverage it is necessary to calculate the reading probabilities on the results from the largest possible sample size. It is presented how the statistical margins of the coverage are reduced essential by calculating the reading probabilities on a yearly basis and on media group levels. Finally the paper illustrates how the calculation of duplication, sole readership and non-readership are more complicated by using reading probabilities. But the consequences of using probabilities instead of traditional 0-1 variables are much more realistic results.