Top: FWHM of the CCF as a function of binary period and a red dashed trend fitted to the data for P< 8 d. Roughly beyond this period the primary stars are rotating slow enough such that the instrumental broadening dominates the rotational broadening, and truncates any potentially continued trend below 7 km s^-1. Bottom: precision of the radial velocity measurements for each binary as a function of binary period. The red dashed line shows the median precision for all binaries within four coarse period bins, chosen for the later study of triple systems in Sect. 6.4.