The new recommendation ITU-R P.1546 replaces the recommendation ITU-R P.370 which will still be valid in the near future. Nevertheless, it is useful to acquire background information on this high sophisticated recommendation. There are some big changes as well as several detailed changes, which have more or less influence on the field strength calculations. Due to the use of this new recommendation for international coordination everyone in the broadcast business should be informed of how to handle the parameters. The use of the terrain clearance angle for example has great influence on the calculation and coordination results. Furthermore, there are some interesting changes in comparison with the ITU-R P.370 like determination of the antenna height, which is not a fixed value any more but is floating according to the surrounding topology. So it is useful for the planners to know the “secrets” of this quite complex propagation model.