1. Bubbles

Most surveying equipment has a bubble to facilitate being correctly oriented to gravity. Two kinds of bubbles are used: bubble tube and circular bubble. Figure E-1 shows top and side view of both.

Top View

Side View

a. Tube

b. Circular

Figure E-1
Bubbles

 

The axis of the bubble tube (ABT) is a line tangent to the center of the upper curved surface of the bubble, Figure E-2.

a. Tube

b. Circular

Figure E-2
Axis of the Bubble Tube


Technically, since a circular bubble is spherical, the ABT is actually a plane, Figure E-3, but we can refer to its edge view as the ABT.

Figure E-3
Circular Bubble Plane