The preceding chapters have laid the foundations for the results that will be shown in this chapter. The ECR magnetometry technique was outlined in detail in Chap.  5 and the gravitational experiment results published by ALPHA in 2023 [1] and shown in Chap.  6 . This chapter pertains to all ECR data used in the characterisation of the magnetic field in those gravitational experiments, namely in setting the magnetic bias at the start and end of a magnetic release plus systematic studies to constrain what the bias looks like between these points. Section 7.1 will discuss selection of magnet currents to produce the desired magnetic field biases, Sect. 7.2 shows the magnetic field measurements made during the release experiments, Sect. 7.3 has details of ECR measurements made to constrain uncertainties along with the techniques developed to acquire those data. Section 7.4 will contain a discussion of how these data were used to adjust the magnetic field model used in simulations of the antihydrogen trajectories in ALPHA-g along with a summary of the final uncertainty values. Finally Sect. 7.5 contains details and results from proof-of-principle ECR measurements designed to inform future higher precision experiments in ALPHA-g.