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Tape calibration
The instrument calibration thread below reminded me of a story from long ago.
A newly licensed surveyor was eager to get his own business started and he wanted to do everything right.
To add credibility to his measurements and have a sense of surety about his work, he took his brand new tape to a calibration baseline.
He measured from “0+00” to “1+00” and determined his tape was too long, by 0.035′ after applying tension and temperature corrections.
He applied that correction to every measurement thereafter.
One day he and some other surveyors were discussing the baseline and he found to his horror that “1+00” was not exactly 100.000′, but was deliberately set 0.035′ short so every tape, long or short, could be used, presuming no tape is manufactured worse off than that. He didn’t realize that baseline points are set and then measured to after sitting for a while. (It would be very difficult to layout exact intervals for a baseline. My baseline, for example, has monuments at 0 +00, 1+49.9768, 4+50.1148, 5+50.1042, 6+00.0924, 10+50.1069 and 15+50.1561, all meters)
He filed a Record of Survey to correct, or at least notify everyone, that all his work from the calibration date to then was off by the calculated error.
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8 Replies
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Dave,
Many times we cannot see the forest, because trees block the view.
SW Arkansas Pedantry Group.
N
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Dave
This is a very interesting story and it shows that a little communication on the new surveyors part
would save a lot of trouble.
It also shows that the organization who established that base line (and it was NOT NGS) did not know what they were doing.
This is very clear by looking at the distances you published above. A very good example of the distances would be the Kingman CBL in
Kingman, Arizona. In 1987 the maximum difference between a multiple of 10 meters on the Kingman base line was 4.6mm ; When it was
recalibrated in 2004 it was 2.3mm. The base line that you use, the difference between a multiple of 10 meters and the published distance
is 156.1mm. If you don’t use the long distance ( 0+00 to 1550.1561) then it is from 0+00 to 4+50.1148 or 114.8mm over. Not good.
JOHN NOLTON
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Iƒ??ve never seen a baseline 150m 50m 1000m that was xxx.000.
The discs are set, then 6 months later they are measured. Who would ever think that a CBL had xxx.000 distances? Ever!
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LARRY SCOTT, I would think you should read my post again. NO place do I say that a base line should be xxx.000 PERIOD.
JOHN NOLTON
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especially when said tree ends up being on line.
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My apologies. I misread it
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That’s OK Larry. I have done the same (misread) more than one post. Hope all is well
with you.
JOHN NOLTON
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I’ve never misread anything!
(Liar Nate)
N
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