Feedback on... SURVEYING
(Page 3 of 4)
November/December 1975
By the Mother Earth News editors
Before I move on, I'll just mention a few other miscellaneous matters covered in Part I of the article. [1] The elaborate note-taking described on page 91 of MOTHER NO. 34 isn't necessary unless 'the survey is to be placed on record. Also, in the same paragraph, Ms. Gelwick mentions "elevations from range pole readings". There's no way to determine elevations from a range pole . . . you must use a leveling rod.
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[2] That instrument in the photo on the same page is a wye level, not a dumpy (which is shown, correctly labeled, in Fig. 8 of Part II). The difference is that the wye's telescope can be removed from its standards, while the dumpy's can't.
[3] According to the author, surveying instruments can be rented by laymen. Though I've never tried to do so, I'm willing to bet that anyone who does will have to put down a good-sized deposit. Such machines aren't playthings and they can be damaged quite easily.
Now to some remarks on Part II. To begin with, I can't say much for Aimee's way of leveling a footing. If the site were on a hillside, she might need awfully long stakes . . . and the string is quite unnecessary.
Another note on leveling: You don't need a tape for this process unless you're cross-sectioning or running a profile (a vertical section through an area to show elevations and depressions). I've performed both those operations with a tape, a 2-foot carpenter's level, a 5-foot stick, and a 6-foot folding rule.
Now a word on the use of the transit. All angles should be turned to the right—as follows—to ensure accuracy: Take the first reading and leave it in the gun. Then turn the same angle twice more, note the third result, and divide the figure by 3. This should give you a mean close to the first reading . . . and if it doesn't, you did something wrong.
You can, of course, turn angles as often as needed for accuracy. It's really best to do so six times, reading the first, third, and sixth . . . then six more times, reading the ninth and twelfth. This method cancels out any error in the instrument.
Incidentally, the stations used in transit work are not bench marks, as Aimee says. A bench mark is a position marked with an elevation, and most geodetic monuments aren't of this type.
I should also point out that there's no use in writing to the U.S. Coast and Geodetic Survey for land measurement information. The only data available from that source are the geodetic positions of monuments, and when you'd found one such marker you probably wouldn't be able to see the next (since most of the Survey's work is done from towers).
