For robust control and fault detection in electrical networks, the network frequency is an important quantity. In rapidly changing (transient) network states, however, the network frequency cannot usually be defined unambiguously and a compromise must be found between a very accurate and a very fast measurement.This VDE FNN note describes the relationships between measurement duration and measurement accuracy according to the current state of knowledge and provides an overview of various measurement methods and their applications. The focus is primarily on grid protection and the note is consequently aimed at grid operators, manufacturers and users. It replaces version 1.0 of the 2017 VDE FNN Note "Determination and evaluation of the grid frequency - effects of grid-side disturbances". The chapters have been reorganized according to functions and areas of application and expanded thematically.This VDE FNN Note was revised by the VDE FNN Expert Network Grid Protection on behalf of the VDE FNN Steering Committee Grid Technology and Grid Operation. It has been coordinated with the VSE Association of Swiss Electricity Companies and the "Protection Technology" working group of ÖESTERREICHS ENERGIE and is published jointly.