單項(xiàng)選擇題當(dāng)采用激光投點(diǎn)儀指示立井井筒掘砌方向時(shí),應(yīng)經(jīng)常對(duì)儀器進(jìn)行檢查,并每隔()用掛垂線等方法對(duì)光束進(jìn)行一次檢查和校正。

A.150m
B.50m
C.100m
D.200m


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