4. Rod Bubble
A rod bubble is a separate bubble typically used to hold a level rod vertically. Because it is similar to a rod-mounted bubble, a few of its checks are related.
a. Use an adjusted pole mounted bubble
After a pole-mounted bubble has been adjusted, it can be used to check a rod bubble, Figure B-8.
 |
| Figure B-8 Using Adjusted Pole-Mounted Bubble |
With the pole bubble centered, the rod bubble is checked. The amount the bubble is outside the circle is the bubble error. Center the bubble using the adjusting screws on the bottom, Figure B-9.
 |
| Figure B-9 Adjusting Screws |
b. Plumb bob
The plumb bob method for checking a pole-mounted bubble, Figure B-7, can also be used for a rod bubble. Use a short section of range or reflector pole.
c. Calibrated door jamb
Use an adjusted bubble to find and mark a vertical door jamb section. The calibrated door jamb can used to check and adjust bubbles in the figure, Figure B-10.
|
|
| Figure B-10 Calibrated Door Jamb |
Check the door jamb periodically with an adjusted bubble.
Because they are inexpensive, it's a good idea to have an adjusted bubble in the office and not use it in the field. It can be used to check other pole-mounted and rod bubbles.