 speed, which has been shown to be inaccurate from archival spectroscopy [@Blundell05; @Blundell11]. Assuming that the subsequent motion is ballistic (this assumption is discussed in Sec\[sec:ballistic\]), and adopting the standard kinematic model [@Hjellming1981], the locations they attain by the Julian Date of the mid-point of the ALMA observations (2457294.4836) are calculated, and plotted in Fig\[fig:combine\]. The assumed parameters of the kinematic model using the notation of @Eikenberry01 and @Hjellming1981 are: cone angle $\theta = 19^\circ$ (Hjellming et al. use $\psi$), inclination $i = 79^\circ$, rotation on the sky $\chi = 10^\circ$ (position angle $+100^\circ$), period $P = 162.34$day (Blundell et al., in preparation) and distance $d =
5.5$kpc [@Blundell04; @lockman2007]. The ejection phase was determined by fitting to the observed redshift pairs from JD 2457000 to JD 2457293.5. The phase $\phi = (2\pi/P)(t - t_{\rm ref}) + \phi_0$ with $\phi_0 =
-0.241$rad for a reference Julian date of $t_{\rm ref} =
2456000$. $\phi$ is used as in equation 1 of @Eikenberry01; @Hjellming1981 denote the same quantity by $\Omega(t_0-t_{\rm ref})$.

Millimetre polarimetric imaging {#sec:ALMA}
===============================

SS433 was observed using 27 ALMA antennas between 2015 September 28 21:26 and September 29 01:46 UT. Three execution blocks were run almost in sequence and under similar conditions. The precipitable water vapour column was around 1.4mm. The correlator was set up in Time Division Multiplex mode with a total bandwidth of 7.5GHz, in four 1.75-GHz spectral windows (spw) centred at 224, 226, 240 and 242GHz. Each spw was divided into 64 spectral channels and XX, YY, XY and YX correlations were recorded. The longest and shortest baselines were 2270 and 43m, sensitive to angular scales $\la 3.7$arcsec.

The quasar J1751+0939 was used as a bandpass, polarization and flux scale calibrator and J1832+0731 was used as the phase reference source on an approximately 8 min cycle. The total integration time on SS43