line of collimation
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line of collimation[′līn əv ‚käl·ə′mā·shən]
In a surveying telescope, the imaginary line through the optical center of the object glass and the cross-hair intersection in the diaphragm.
line of sight, line of collimation
The line extending from an instrument along which distant objects are seen, when viewed with the telescope or other sighting device. Also see sight line.