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When mapping (or reviewing a map, if you are a Certifier) a calibration course, each endpoint must be described precisely. Ideally, there would be two measurements on an endpoint that is not immediately next to a landmark. If the landmark is away from the curb, there should be two measurements (one from each of two landmarks).

The point of the description and measurement is to enable anyone to replace a lost nail. A description of "about 29 meters south of the stairs" is not anywhere close enough for a calibration course endpoint description. We adjust for temperature when we tape a course, which may move the point ½" or ¼". "About" has no place on a calibration map. Please make sure that all calibration maps have good, precise descriptions of each endpoint, so you or I could take a tape out and replace a lost nail.
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I am with Paul & Jay 100% on this one. I was always taught, "if you can't find the nail, don't use the course." Some measurements from landmarks are very obvious; others, not so much. We should not depend on descriptions to relocate a nail, even on our own cal courses.
I have one cal course where snowplows seem to catch my endpoint every winter, even though I use a PK nail driven flusher than flush. One year I found a clearly demarcated divot and put in a new nail, but another time could not so remeasured.
It's a great teaching opportunity for new measurers, since we don't often lay out cal courses. And since an accurate cal course is the foundation upon which all other measurement accuracy is based, it only makes sense to do it properly.
Guys, I stated it as I did, to make the point that we need precise measurements. If I said "so we can find the nail, if it exists", it could be interpreted as "even-feet in the description is good enough, especially if there are two measurements. If one can't find the nail when that close, then it must not be there."

I suppose shouldn't have stated it that way, as it gives the impression that it is okay to replace nails on calibration courses.

I am with you, though - if I can't find a nail, I re-measure. However, when I did, I was about 6" away from the described point, even after two measurements. It wasn't my cal course to start with, so I went with my measurements, and submitted for a new cert.
"about 29 meters south of the stairs"
This is probably my calibration course on the Heartland Bicycle Trail in Park Rapids, MN. Those stairs do not meet the bicycle path. The point on the bicycle path adjacent to the south end of those stairs can only be estimated to within a foot. There is no other landmark within 150 meters of that calibration course nail. If I did this again, I would measure in feet from stairs to nail.
I believe there should be a great accuracy to the measurement from stationary objects. I helped measure a course where the nail of the calibration course was only two feet from the start of the race. We decided to double nail the race course to prevent confusion. Noting it on the race description, since it was measured years after the establishment of the cal course is the only way anyone else using my course would know which nails to use.
I am currently re-measuring to shorten the calibration course in front of my house. One endpoint is on a concrete street, so I can't very easily put a nail at the location. I will describe the endpoint relative to expansion joints on either side of it, and then describe the location of the expansion joints relative to driveway edges.
I think if someone described the endpoints relative to at least two landmarks on the surface of the road , I would trust it enough to use it even if there was no nail.
I'd be interested in comparing notes regarding making permanent marks in concrete pavement.

The calibration course near the finish line of the Chicago Marathon is set on a concrete sidewalk. The ends are marked with holes driled in the concrete in a cross pattern. When the paint on the ends of it fades, we all lay some more down so they'll be easier to spot.
It's an important course because it's used to calibrate for almost every measurement in or around the Chicago Loop; it wouldn't surprise me to find that it's used 20-25 times a year.

The course needs to be remeasured by the end of 2013 if it's going to remain certified, and I'd love to find a more elegant way to mark it. My thought is to drill a hole deep enough to accept the entire nail, then drill a larger concentric hole that would accept the head. I'd then drop a nail in the hole and secure it with epoxy. If I could get the nail head flush with or below the top of the sidewalk, I can't imagine the nail going anywhere.

Anybody have any experience with this or anything like it?
Whenever I've tried to put nails into concrete the concrete chips away.
Jim, I guess I could have put the endpoint at the expansion joint, but my point was that expansion joints might move too if there is construction. But even if the driveways and the expansion joints all move, there's no real chance that all those measurements I give to landmarks would all still be the same, so someone trying to use the course would know something is wrong.
I once found one of Jim's end point nails under 1-1/2-inch of new blacktop. I wasn't so lucky on the other end and remeasured,

As for marking endpoints in concrete, I carry a 3/4-inch star drill (also works great as a peg when steel taping). I "drill" a 1-inch deep hole in the concrete and fill it with paint. This makes a pretty permanent mark.

There's a question on the cal course application that asks if the end points are marked such that a bicycle can touch them. To me that means a permanent mark of some kind.
My primary calibration course was repaved a couple of years ago. The previous description was from a utility pole at a slight angle. That did not match what I thought was old paint that had extended onto the concrete gutter. So I redid the whole thing. Then, I referenced to TWO expansion joints so as to not rely on the + - 5 degrees of compass accuracy. Only if those two measurements agree, will I have enough confidence to NOT remeasure the whole course.

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