This is an interesting variable magnification optic that links the selected magnification with the BDC for 7.62x54R to a specific distance.

While most variable power optics zoom in on the target but maintain the same zero, 1P21 actually adjusts the BDC based on the zoom. What happens, and what is very confusing to most Westerners, is that you use the range finder in the reticule to estimate distance, then dial the magnification to that range which puts the BDC where it needs to go. It is intended to help the shooter get a good sight picture and proper BDC quickly and easily, and if you understand how the optic works it does exactly that. However if you increase magnification but the target is not at the correct distance the point of impact will change and you will either hit the target high, or miss altogether.