I just used a laser plummet to mark two points in a door jam, then placed the rod on the bottom point and (with a point on the top of the rod) extended it to the upper point. It can then be rotated and the bubble observed in different positions. This is the same method I was taught years ago except I used a plumb bob then instead of a laser.
This, however does not ensure the rod is true or straight. I guess if it were bent the bubble would move? Any other/better methods?
If the pole was significantly crooked or bent you'd never be able to get the bubble to stay centered through 360 degrees of rotation.
We have one of those wall mounted things but I was taught years ago that in a pinch you can level it up in the 90 formed by the back of the truck and the lowered tailgate and rotate it carefully... always taking out 1/2 of the error with the adjusting screws and 1/2 by re-leveling.
Never did the truck thing, but in a 2-man crew we used to verify plumbness by sighting through the gun then rotate the pole in 90° increments and observe again. That didn't adjust anything though....just let us know there was a problem.
We use a True Plum. At another place. We drilled a small hole in the door jam and another in the floor. We screwed a prism pole point onto the top. We then extended the rod so we had a point in the top and bottom hole and rotated the pole. I have always used the low tech plumbbob for this task as those laser thingys can get out of adjustment. I hope this does not cause a discussion about accounting for the RPA of a plumbob in StarNet.
> We use a True Plum. At another place. We drilled a small hole in the door jam and another in the floor. We screwed a prism pole point onto the top. We then extended the rod so we had a point in the top and bottom hole and rotated the pole. I have always used the low tech plumbbob for this task as those laser thingys can get out of adjustment. I hope this does not cause a discussion about accounting for the RPA of a plumbob in StarNet.
I used more than one laser to be safe. I work for a construction company so there are probably 10 of them around here.
The weather has been so bad around here I will expect all local field crews to have fully calibrated total stations, tribrachs, prism poles, pegged levels, full cans of paint, full rolls of flagging, and plenty of stakes and nails in the truck. You know that's not the case though....sadly it doesn't seem to work that way anymore.:-/
One time I could easily see that the pole was not plumb, even though the bubble said it was. So I just plumbed it up (sighting an edge from about 20 feet away, turning it 90 degrees, re-sight, re-plumb etc) and instead of trying to field adjust the bubble, I just took a sharpie marker and made a Sharpie dot at the center of the bubble location. My temporary Sharpie dot worked for the rest of the day and I did a proper adjustment later, back at the office.
> Any other/better methods?
I don't think that using a prism pole *tripod* in the field can be beat. It sets up quickly on control points and boundary markers and the pole can be rotated in it to either verify that the bubble is in adjustment or to adjust the bubble as needed in the field.
So that is SOP and with an 8-minute vial in the pole it keeps centering errors below 1mm for target heights in the 5 to 6 ft. range.
True Plumb jig, All crews check each pole on their truck every Friday and we switched to the 8' bubbles.
We set two instruments up 90° to the pole and check it that way.
I have three 2-section rover rods (2m) that are not perfectly straight and I have one of those jigs that hold the point at the bottom and have 2 adjustable screws in a bracket to level the pole. I put the bracket with the screws up high, near the top of the rods.
Adjust the screws so that the bubble stays in the same place in the vial as you rotate the rod. This means that the top of the rod is centered directly over the point.
Then adjust the bubble to center in the vial. It should stay there as you rotate the rod.
I have the upper and lower rod sections numbered so that the same top and bottom always get put together the same way. The lower section has male threads on both ends and I remove the points for storage so I have the point end of the lower sections labeled so the point is always on the same end.