Binary lens geometry projected onto the sky in the complex form. The binary lens is at z₁ and z₂. The source star is at w, and the direction of the relative proper motion is shown as ﹩{\hat{{\boldsymbol{\mu }}}}_{\mathrm{rel},\odot }﹩.The angle α is defined as the angle between north and the binary axis. α increments eastward of north. ﹩{\phi }_{{\pi }_{E}}﹩ is the angle east of north of ﹩{\hat{\mu }}_{\mathrm{rel}}﹩ and also ﹩{\hat{\pi }}_{E}﹩.