The optical procedure being done is used for:
Ans. (d) Subjective refinement of cylinderRef: Khurana optics 2/e, p. 153The instrument seen in the image is the Jackson cross cylinder (over the trial frame) - which is used for subjective refinement of cylinder.
Objective refraction
Subjective adjustment of cylinder
Binocular balancing of vision
Subjective refinement of cylinder
Elementary Optics