The Sentinel combines the traditional Yukon style of perfect design, ergonomics, reliability and easy and convenient use with an enhanced level of functionality. This incredible riflescope has a high IPX4 grade of water-resistance and can be operated in extremely precipitous situations while functioning normally and without causing damage to the unit. Extra tube protection provides durability towards the axial load when used with the majority of popular calibers, including .300, .308 or similar. The 2 AA batteries are placed in the battery compartment vertically, thus eliminating the influence of recoil on the stability of the energy supply. The Sentinel has two scales, a horizontal scale to measure the distance to a target and a vertical scale that facilitates adjustment when shooting at different distances. Initially, the riflescope should be sighted at 50 m on the central crosshair; the distance is determined by putting a target with a known width (0.5 m) between the >..< marks. If the target fits between the marks, the user should make the vertical adjustment according to the mark. So, the user can make adjustments when shooting at distances of 15, 25, 50 and 100 m. It is advisable to change the color of the reticle, depending on the surrounding conditions. Red is best when used in clear viewing conditions, green is preferable for use when viewing is obscured and the color can be changed by the simple push of a button. The riflescope has an extra 7/8 Weaver rail placed on the left side of the body and is designed for mounting accessories (IR illuminator, directional microphone and laser pointer). The image focusing mechanism (from 2 m. up to infinity) with fixation of the focus ring knob at the mark 100m , provides clear image at any distances (including short) within the riflescope's working range.