Top to bottom: Post-fit timing residuals for NGC 1851A obtained with the DDH timing model, as a function of (a) epoch and (b) orbital phase. The orbital phase 0 denotes periastron and the residual 1-σ uncertainties are indicated by vertical error bars. The various colours denote the different telescopes and backends used for the timing. Orange indicates the early GBT data, and purple and red indicate the uGMRT data taken in the PA and CDP modes respectively. Grey and green represent the data taken with the L-band and the UHF receivers of the MeerKAT.