I ri-parallaxed my competition (2 40x) from 8 meters and focus up to about 55 meters.
Ri-parallaxed distance estimation doesn't becomes more accurate, it simply has more space on the wheel.
For ri-parallaxed must first loosen the outer ring in front of the front lens and move forward to the second ring by turning it to the left.
This is quite easy and totally reversible, the only difficulty may reside in unloose the first ring nut which is sometimes close with a lot of force.
To do this without doing damage must equip itself with a key made with a simple piece of sheet metal but very accurate to avoid damages.
This is my key