Prism Pole Calibration Using a Tribrach

I've wondered if a simpler approach to this is to use a torpedo level on side of the pole in clay dirt so bipod and pole firmly in place. Check on all sides of pole with torpedo level to get plumb, then adjust the bubble. Means you can do it with pole up and torpedo helps you isolate any 'run out' in the pole to.

@lukenz What is the sensitivity of a torpedo level? Levels from a manufacturer such as SOLA in Austria have specified sensitivities, but with a level from the local do-it-yourself store, who knows?

I still love the plumb bob method. We used to check adjustment all the time with the instrument man plunging the rod, the rodman spinning it 90.

That's a pretty cool option that I'd never thought of before, but I still would not like to be without a "Stedi-rest". Cheap, like borsht. Easy to keep in the glove compartment.

Amazon.com: Stedi-Rest : Everything Else

(Today's Amazon price is crazy high, I think I paid $12 for mine.) 

S L I C K !

Posted by: @norman-oklahoma

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Amazon.com: Stedi-Rest : Everything Else

(Today's Amazon price is crazy high, I think I paid $12 for mine.) 

It looks like they stole the image from Baseline Equipment, who has it for $17.65. https://www.baselineequipment.com/seco-stedi-rest

That procedure makes an assumption your tribrach is in alignment, i.e. interjects another source of error. Just hang a plumb bob from a doorframe/tree branch whatever

Posted by: @james-vianna

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That procedure makes an assumption your tribrach is in alignment, i.e. interjects another source of error. Just hang a plumb bob from a doorframe/tree branch whatever

Plumb bobs are always calibrated,,,,,,,,unless it's windy,,,,,,,,unless you're hung over. 😉 

Posted by: @wendell

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It looks like they stole the image from Baseline Equipment, who has it for $17.65

That's more like it. 

The best method I know to check and adjust a pole bubble is to use a doorway. 

Make a mark on the lintel. Transfer this mark to the floorplate with a plumb bob.

Now you can wedge your pole between the two marks, and can spin and adjust to your heart's content.

Its even easier if you have a spare pole tip you can place on the top of the pole.

Posted by: @james-vianna

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That procedure makes an assumption your tribrach is in alignment, i.e. interjects another source of error. Just hang a plumb bob from a doorframe/tree branch whatever

It does & it should be. If we're willing to accept a tribrach out of calibration to choose a method of hanging a plumb bob from a tree I would argue your setup is still fraught with error sources that it really shouldn't be.

Next weeks video is on how to check/calibrate a tribrach in the field, again, without special tools. Just one video in what will soon be a library that will hopefully cover a lot of basics in time for those new guys coming up.

Thanks for the tip BC, almost 40 years into this profession and had never seen this.  I will say that it probably won't work for the vertically challenged.

Posted by: @john-putnam

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Thanks for the tip BC, almost 40 years into this profession and had never seen this.  I will say that it probably won't work for the vertically challenged.

Yea it works sometimes, others not. Im 6' and I'll still stand on something to make it easier for taller poles but even then sometimes it's easier sighting the pole tip and plunging up. For me at least.