Concept:The theodolite is a precision surveying instrument that measures both horizontal and vertical angles.
Explanation:A theodolite is designed to measure angles precisely in both the horizontal and vertical planes.
Its telescope rotates around both axes, allowing the surveyor to sight different points easily.
The instrument has graduated circles, one horizontal and one vertical, from which angle readings are taken.
It is widely used in surveying, engineering, and construction for tasks such as triangulation and traversing.
The other listed tools serve entirely different purposes.
A Gunter's chain measures linear distances on the ground.
An offset staff is used to measure short offsets from a baseline.
An arrow is a pin used to mark the ends of chain lengths.
None of these can measure angles.
Thus, the correct instrument for measuring horizontal and vertical angles is the theodolite.
Answer:A. theodolite