An optical square is used for the same purpose as the cross-staff, but it is more accurate.

Name: An optical square is used for the same purpose as the cross-staff, but it is more accurate.
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Question

Quizplus · Accepted Answer

An optical square, utilizing prisms or mirrors to reflect images, provides a more precise method for establishing right angles or perpendicular lines compared to the cross-staff, which relies on direct sighting and is thus less accurate.

An Optical Square Is Used for the Same Purpose as the Cross-Staff