Upright posts for a Marble's Improved Tang Peep Sight are interchangeable and of different heights to correspond with different shooting range distances. The approximate effective maximum distance for each upright post is as follows: Short Range: 0-100 Yards (1.619" to 1.924" height adjustment range; 0.5" aperture disc with .055" peep). Standard: 30-250 Yards (1.856" to 2.352" height adjustment range; 0.5" aperture disc with .055" peep). Mid Rang: up to 500 Yards (2.347" to 3.364" height adjustment range; 0.5" aperture disc with .055" peep).