A standing opaque beacon may be useful in addition . 此外，也可以使用常设的实体觇标。
2.
Based on the statistics of the double observing date of tunnelsurveys , the paper analyses the targets affect sighting errors and points out the ways of the selection of targets and the questions needed to attention in observing 根据隧(巷)道双次观测值的统计资料，分析觇标对瞄准误差的影响，提出觇标的选取方法和观测中注意的问题。
3.
Permanent surveying markers as referred to in paragraph 1 of this article include wooden or steel signals and stone markers established at triangulation points , baseline points , traverse points , military control points , gravimetric points , astronomic points and leveling points of various orders and classes , as well as fixed markers used for topographic mapping , engineering surveying and deformation measurement , and installations at seabed geodetic points 第一款所称永久性测量标志，是指各等级的三角点、基线点、导线点、军用控制点、重力点、天文点、水准点的木质觇标、钢质觇标和标石标志，以及用于地形测图、工程测量和形变测量的固定标志和海底大地点设施等。
