It certainly seems "jumpy" enough to be the former. Is there a way to tell?
I'd set my tribrach on a 2x4 or other fairly stiff item and level it. Then use shims to raise one end of the 2x4 until the bubble moves the required amount and calculate the angle from arctan(HeightChange/Length) For 8' that would be a little less than 1/4 inch in 8 feet.
Now, educate me. How far does the bubble of an 8' vial move when it is 8' off level? Is it a specified distance, and the bubble centered on a line at that point?
Edit: I didn't read carefully, so I'm not sure how you could mount the vial, but you get the idea - you can rig something up.
OR, put a piece of tape on a door frame about 5 ft up. Hold your pole so the bubble says level, and mark the tape. Move it until the bubble is the required amount off, and mark. Measure the distance between marks. At 5 ft, 8 minutes is 0.14 inch.
Check the manufactures’ catalog. It will say what vial is in the pole. Typically it is a 40 minute vial. My Leica can with an 8 minute vial. I have changes my Seco’s 40 minute vial to 8 minutes.
> I'd set my tribrach on a 2x4 or other fairly stiff item and level it. Then use shims to raise one end of the 2x4 until the bubble moves the required amount and calculate the angle from arctan(HeightChange/Length) For 8' that would be a little less than 1/4 inch in 8 feet.
>
> Now, educate me. How far does the bubble of an 8' vial move when it is 8' off level? Is it a specified distance, and the bubble centered on a line at that point?
>
> Edit: I didn't read carefully, so I'm not sure how you could mount the vial, but you get the idea - you can rig something up.
>
> OR, put a piece of tape on a door frame about 5 ft up. Hold your pole so the bubble says level, and mark the tape. Move it until the bubble is the required amount off, and mark. Measure the distance between marks. At 5 ft, 8 minutes is 0.14 inch.
One thought I had was to remove it from the pole, place it on top of the telescope of my total station; level it, then raise or lower the telescope by "x" minutes. But how far is the bubble supposed to move? One full diameter in the specified precision? half a diameter? Something else? What is the "required amount"?
A Google search for "8' circular level spec" turned up a couple of manufacturers web sites with the following statement: The sensitivity of a level is defined as the change of angle or gradient required to move the bubble by a set distance (usually 2mm). If the vial has graduated divisions then the sensitivity refers to the angle or gradient change required to move the bubble by one of these divisions (often spaced at 2mm).
These were industrial equipment suppliers not surveying equipment suppliers but both quote it as an industry standard.
Here's a graphic from one of the sites:
> Check the manufactures’ catalog. It will say what vial is in the pole. Typically it is a 40 minute vial. My Leica can with an 8 minute vial. I have changes my Seco’s 40 minute vial to 8 minutes.
Don't have the manufacturer name. Bought it used.
> A Google search for "8' circular level spec" turned up a couple of manufacturers web sites with the following statement: The sensitivity of a level is defined as the change of angle or gradient required to move the bubble by a set distance (usually 2mm). If the vial has graduated divisions then the sensitivity refers to the angle or gradient change required to move the bubble by one of these divisions (often spaced at 2mm).
>
> These were industrial equipment suppliers not surveying equipment suppliers but both quote it as an industry standard.
>
Thanks. It's got a single circle, so I just plumbed the pole, against a table, then tilted it until the bubble moved about 2 mm, and measured how far away from the table the pole was, and did an arctangent to the floor.
Looks like it's a 40' vial.
The sensitivity of a vial is expressed as its "PAR"
"PAR" is abbreviated with the Greek letter "pi." Par is the vial's sensitivity in arc seconds or arc minutes per graduation. For a tubular vial, the amount of perpendicular tilt to the axis of the vial is termed "WIND," which rhymes with "bind." Instrument shops, particularly manufacturers calibrate level vials with a "Level Tryer."
In geodetic observations, highly sensitive vials that are calibrated, normally have a secondary chamber so that the observer can keep the length of the bubble constant as the ambient temperature changes since a vial is calibrated with a certain par length, generally twenty par. For geodetic astronomical use, as the night's temperature cools, the bubble has to be periodically lengthened to keep it at twenty par long.
Bullseye bubble vials are so coarse that calibrations are rarely done, if ever.
The most elaborate use of level vials in geodetic work is with the "Horrobow-Talcott" method, used with first-order theodolites. Furthermore, blah, blah, blah ...
The sensitivity of a vial is expressed as its "PAR"
PAR (Pars) is old terminology and has not been used by manufactures in over 50 years.
A Par used to be 2.2558 mm = one Parisian line. All manufactures use 2mm for the distance between lines on bubbles.
See Surveying Instruments by Fritz Deumlich page 54, 1982.
Some references will also say that the distance was 0.1 inch (2.5mm), see Surveying by Davis & Foote 4th edition, 1953 page 15.
If in doubt measure it.
I am not sure how to spell the instrument that calibrate the level vial but I have seen it as trier(?) I could check some other references but I will leave it to the spelling police here on the board.
JOHN NOLTON
Tombstone, AZ
The sensitivity of a vial is expressed as its "PAR"
Interesting details; thanks. What I wrote was off the top of my head, but the actual distance between the lines on my Swiss striding levels seem to be larger ... if memory serves me correctly (T-4, BC-4, DKM-3A). I'll be breaking out my toys for class in a few weeks, I'll have a look at that.
Prof. Cliff Mugnier
Cliff when you check your bubbles on the T4 also let me know the approx. year it was built. The Kern DKM3 and the Kern DKM3A use the same striding level and both of mine are 2 mm between lines.
Thank You
JOHN NOLTON
Tombstone,AZ.
If you center the bubble inside of the typical bullseye circle found on a prism pole (as the original post suggests), is the angular specification of the bubble vial the angle (in minutes) that the prism pole would tip until the edge of the bubble first touches the circle??ÿ In other words, is the angle from center to edge, or edge to edge?
a 40 you can hold plump all day long with the 8 you are saying what is taking so long to get this shot, I can't hold this plump any longer.
Also I think they are different colors
I had found this and saved it about a year ago. It may answer your question
https://www.leveldevelopments.com/sensitivity-explained/
An 8' pole is 8 feet long. And, a 40' pole is 40 feet long. And, the difference is 32 feet.
Keep your cool. 🙂
N