Sphere Neutralization:
with a cross target image, lens moving along the power meridian,
- if minus is the power, "with" movement is observed;
- otherwise; "against" movement observed.
Note that only the line oriented perpendicular to the lens movement shows movement.
Cylinder Neutralization:
with a cross target image, lens being rotated at a certain direction,
- if minus is the cylindrical power at a certain axis, the image of the line along the axis shows "with" rotation;
- if plus is the cylindrical power at a certain axis, the image of the line along the axis shows "against" rotation.
Generalization:
Pick a "Reference Line", observe the image of the "Reference Line" along which the axis of the interested cylindrical power orients.
Both displacement & rotation of the lens give the same "generalised" observation:
- if minus is the power, "with" movement is observed;
- otherwise; "against" movement observed.
Spherical lens can be considered as cylindrical lens with identical cylindrical powers along different meridian.
