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Backsight elevation check values  

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Reece_125
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Hi Gents,

I’m not sure if this issue has been covered else where, but I have looked high and low. 

I have an issue when ever I set up on my foresight and check back to my backsight I’m constantly getting up to 10mm vertical difference over only 100m.

I have taken direct and reverse readings when foresighting the point in. 

I performed the check and adjust routine only 2 days ago. 

Im using a 5” Ts 15 , Leica round prisms,  on a Leica pole and bipods, Leica GHM007 tape with tribrach hook. 

It’s been driving me crazy trying to find the issue. 

Cheers

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kjypls
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Have you measured (with a tape measure) the actual pole heights to make sure they are what the pole says it is, or what you assume they are?

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Reece_125
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Yes, I measured the pole before I started. The pole tip is a little worn, so it read 1.298m

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Paul in PA
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Some instruments require a regular vertical circle calibration. First check, is to check your backsight with both faces, same as setting your foresight. Vertical circles are generally no locked to the EDM base but instead have gravimetric base with electronic calibration.

Paul in PA

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Reece_125
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I ran the tilted axis routine 5 days ago. And it got used once for the week for about 30mins. I did notice that the delta height difference when foresighting point in was about 8mm different in each face.

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Steven Metelski
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Just to eliminate the obvious...

Leica instruments do not measure to the center of the scope for height. It has a special braket and tape to measure down.

Your IH would be higher by roughly a tenth or two (memory is foggy) if you measured to the center of the scope

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Reece_125
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I’ve always used a normal tape measure in the past, and measured to the little dot on the side of the unit. I have recently purchased the genuine Leica GHM007 tape measure & GHT196 tribrach hook. I hoped that is was the issue, but the difference in heights still exist. 

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Jim Frame
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Leica instruments do not measure to the center of the scope for height.

??

t

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Reece_125
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That’s the dot I measure to. Ive compared the Leica tape against a couple normal tapes, and there’s 4mm difference in measurement . I assume that’s because the Leica tape is calibrated for slope. 

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