Extensive power tests of the LHC dipole magnets required the development of new techniques to study the quench and training behaviour. Magnetic measurements of short and long model dipoles have allowed to understand and quantify the time dependent behaviour of the field quality during the current flat top needed during beam injection. The experience gained is employed for the design of the measuring tools presently under construction for the series measurements of the LHC dipole magnets. The economically important issue of how many magnets have to be measured in the superconducting state is addressed in view of the field quality required for the performance of the LHC.