Unfortunately, the desired output should actually be the negative of our original choice for VO in Fig. 1. Thus, a sign error also appears in Eqs. (13) and (14) and of the text. The desired outputs are:
$VVDP0°−VVDP90°=VVDP[3.16π44(σ11′−σ22′)]$
(13)

$VVDP+45°−VVDP−45°=VVDP[3.16(2πD)σ12′]$
(14)