GPO PASSION 8x56 Manual De Instrucciones página 23

Adjustment of the interpupillary
distance (ipd)
Interpupillary distance (IPD) is the distance between the center of
the pupils of the two eyes. For a full "field of view", the IPD of the
binocular must be adjusted to match the IPD of the user. This can
be accomplished by simply opening or closing (buckling) the center
hinge of both binocular halves while looking through the binocular.
The IPD adjustment is correct when you can see a clear single
circular picture with both eyes open.
EN