optical sag视光垂度opticaladj.视觉的；光学的Optical Beam Steering光束操纵optical fibre circuit光纤环网optical fiber/IGBT光纤／绝缘栅双极晶体管optical density value光密度值optical fiber splicer光纤熔接机optical memory system光学存储系统optical-path length光学距离optical beam splitter光束分光镜optical solid circuit光集成电路Optical Fuzing System光引信系统

1. With the range finder a bar with marking the several fixed distances must be affixed to the base of the tree.
   使用视距器时，必须在树基部附加一根指示几种固定距离棒。