Understanding Cross Staff Variations

A cross staff is a surveying instrument used primarily for setting out lines at right angles to a main survey line. It's a simple tool often used for preliminary work or checking right angles in the field.

Typical Types of Cross Staff

There are several typical variations of the cross staff:

• Open Cross Staff: This is the simplest type. It consists of a staff with two pairs of vertical slits or sights cut at right angles to each other at the top. It allows sighting along two perpendicular lines simultaneously.
• French Cross Staff: This is more versatile than the open cross staff. It typically has eight octagonal sides with slits cut to provide sights at angles of 45° and 90° to each other. Some variations might offer 45°, 90°, and 135° angles.
• Adjustable Cross Staff (or Optical Cross Staff): This type usually consists of a cylindrical box with slits or mirrors and lenses. It allows for setting out not just 90° angles, but also other angles by adjusting the position of the mirrors or lenses. It provides more flexibility.

Identifying the Non-Typical Variation

Based on standard surveying literature and practice, the commonly recognized typical variations of the cross staff are the Open cross staff, French cross staff, and Adjustable/Optical cross staff. The term "German cross staff" is not typically listed as one of the standard, widely recognized variations of this surveying instrument.

Therefore, among the given options, the German cross staff is not considered a typical variation.