i Register
In some senses, cross-staff is marked as obsolete, historical. Watch for register when choosing this word.
cross-staff
noun 2
Definitions
noun
1
An archbishop's cross.
2
An early instrument, consisting of a wooden rod with a sliding crosspiece, used for measuring the altitude of a star or for surveying.
The cross-staff is a very simple instrument, a calibrated shaft along which a bar slides.
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