DM variations in the direction of PSR J2219+4754. The vertical line indicates the time at which the last change to the centre frequency and bandwidth of our data occurred, i.e. all data to the right of the dashed line have identical bandwidth and centre frequency (except for slight deviations due to variations in RFI excision). The two arrows indicate the observations that were used to quantify the effect of scattering (see Sect. 3.3), with the latter of these two (MJD 57161) also being the standard template. A DM baseline of 43.48205 cm⁻³ pc has been subtracted. The additional error bars on the lower end of the pre-MJD 57000 data points indicate the expected impact of profile scattering, as described and quantified in Sect. 3.3. The second y-axis indicates the corresponding dispersive delay at an observing frequency of 1.4 GHz.