Evolution of the DM of PSR J2055+3829 as a function of time. Data points shown in black were determined by fitting constant DM values to 50-day segments of NUPPI timing data. The NUPPI observations were split into four sub-bands of 128 MHz each to allow for the fit in DM. The dashed line shows the best-fit DM model, as determined in the timing analysis (see Table 1, “Single template” column). The data point at MJD ∼57600 corresponds to a time interval in which only high frequency (2.1 and 2.5 GHz) observations were available, hence the large DM uncertainty.