The methods can be explained based on the study of Hofmann and Bielschowsky in 1900, who applied a modified Maddox wing: the right eye is presented with a horizontal scale and the left eye with an arrow. The observer perceives that the arrow points onto one of the numbers on the scale which indicates a possible vergence mis-adjustment.
The methods can be explained based on the work of Hofmann and Bielschowsky in 1900, who used a modified Maddox wing to assess eye alignment. The right eye was presented with a horizontal scale, while the left eye received an arrow.  Observers were able to identify which number on the scale corresponded to the arrow's direction, indicating potential misalignment of the eyes.