AN/PEQ-16A or B
US Marine Corps Training Command
<a rel="nofollow" class="external text" href="https://www.trngcmd.marines.mil/Portals/207/Docs/TBS/B1E0795%20Observation%20Theory%20and%20Optics.pdf">OBSERVATION THEORY AND OPTICS B1E0795 STUDENT HANDOUT</a>