At 15 GHz the image resolution is insufficient to confidently distinguish between the compact region components, and so we limit ourselves to reporting the integrated flux density and fractional polarisation values instead. The positional uncertainty is of the order of ≤2% for E in the east–west and north–south directions, and ≤7% in the east–west and ≤60% in north–south direction for W. Here, C is fixed at (0, 0). The uncertainties of the flux density measurements are of the order of 20% at 15 GHz, 30% at 43 GHz, 50% at 86 GHz, and 15% at 228 GHz (The Event Horizon Telescope Collaboration 2019c). The large relative uncertainty in the fractional polarisation of W is related to its small total flux density. The FWHM and positions of the 43, 86, and 228 GHz components have been fixed in the multi-frequency template-matching framework. Error margins indicate the 68% confidence level.