The directions can be obtained by removing the quarter-wave plate and following the procedure for plane polarized light or by interpolation. 可将四分之一波片卸去,并按平面偏振光法或内插法来决定其主应力方向。
The orientation of the principal stresses relative to the directions of the polarizer and first quarter-wave plate is of course immaterial. 主应力相对于起偏镜和第一个四分之波片方向的方位,当然是无关紧要的。