Spectral diagram of the total proper motion of the predicted population for the M14 population. Lines of different colours indicate different distance-limited sub-samples. Dashed lines indicate where the distance-limited sub-sample of the same colour is the same as the next smaller limited sub-sample. Grey areas indicate the proper motion of the three population candidates as labelled. The PMs of US 708 and J2050 relatively similar, so their corresponding lines were unified for legibility. Proper motion errors are of the order of ∼ ± 0.2 mas yr⁻¹ for US 708 and J2050 and ∼ ± 0.1 mas yr⁻¹ for LP 398-9 (Gaia Collaboration 2021).