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After 40 years of measuring I finally set up a calibration course by myself today.
I had to measure a marathon & half about a two hour drive from my home and no one willing to make the trip. Pete had come up with a method but I decided to re-invent the wheel (didn't research what he did).

1.Screwed an eyelet into the end of a plank of wood approximately 4' x 8" x 1"

2. Placed the wood on the ground with the end about 6 inches from the start of the calibration course.

3. Drove one of the tires onto the blank.

4. Using a plastic tie, attached the end of the tape to the eyelet.

5. Place a piece of white tape (vinyl) under the end of the tape. Pulled the tape and marked the zero point.

6. Rolled out the tape, pulled, and marked the 100 meter point.

7. Rolled back the tape and checked that the zero point had not moved - it didn't. Cut the plastic tie, packed up and drove down to the 100 meter point.

8. Repeated the process with a new plastic tie. This allowed me to adjust the distance of the eyelet to the new zero point. I thought about leaving the tape attached to the eyelet when transporting but I thought the wood would shift a little when I drove up on it.

One snag: I was setting this up about 2 feet from a curb on a nice straight road. At the end of the first 100m segment there were leaves on the ground and it was too damp to hold the vinyl tape. Used my little retractable 12 foot tape and placed marks 4 feet from the curb (beyond all the leaves) every 5 meters along the entire 300m calibration course. Started from scratch.
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Very innovative technique, David. I like the solid anchor idea.

If you don't mind doing some math, you could leave the zip tie attached to the eyelet. And, if you have a two-sided tape (ie. one side with metric units and the other with imperial units), you can get the two required measurements in one pass. (I borrowed part of this method from Pete.)

The process would go something like this.
  • place a piece of vinyl tape onto the road and mark the starting point.

  • position the tape so the first mark is somewhere between 0 and 1 meter. Record that value. (If you have a two sided tape, flip the tape over and record the mark on the reverse side.)

  • pull the tape to between 99 and 100 meters and mark the point on a second piece of vinyl tape. Record that value. (If you have a two sided tape, flip the tape over and record that mark.)

  • calculate the metric distance. (If you have a two sided tape, calculate the imperial distance.)

Repeat until you have your approximate distance. Calculate the average distances from the two sides of the tape and then do the temperature adjustments.

That it. -- Justin
Justin, maybe I am missing something in your description. But, I don't see how using a double-sided tape satisfies the 2-measurement process.

If you mis-anchor for one pass, say 1 foot short, both sides of the tape will still show you have enough length. So, you may measure what you think is 1,000', or 304.8 meters, but it is actually 999' or 304.45 meters. Appears that you have measured correctly, but without pulling the tape a second pass, you may make a mistake.

Same concept as me using both an electronic counter and a Jones counter at the same time, and riding a course once. Both counters say I rode the right distance, but if I made a wrong turn, or swung too wide, or cut a corner, it won't show - my course would be wrong.
I've been intrigued by this question about a one-person layout also. I did it once, and I think I essentially did a version of Pete's method. At the recent seminar organized by Mike W and company, I asked Pete about a demo of that, but we didn't have time for it as it turned out.

My question for Dave: what did you have to pull against, and was the system strong enough? (sounds like you pulled against the vinyl tape?)

I have the same reservation as Duane about counting that (Justin's method) as two measurements-- it's just one measurement in two languages I think.

I usually manage to con the race director into helping me lay out a cal course when I need it. One advantage of that is that it pulls them into the whole world of striving for accuracy, and they usually feel good to be part of the process.
A few years ago there was a guy who posted who built a big sled out of 2x4s and cinder blocks to use as an anchor. People pointed out that transporting the thing to measurement locations might be an issue. But David has solved that problem by using the transporter as the anchor!

I still think you missed a great photo-op though, of looking down the length of the tape just as you are preparing to make your mark, and seeing the vehicle holding the tape at the other end.

After this posting I am now anticipating getting a calibration course application from some measurer with the second name on the steel tape data sheet listed as "Chevrolet Silverado."
quote:
Originally posted by Duane Russell:
If you mis-anchor for one pass, say 1 foot short, both sides of the tape will still show you have enough length. So, you may measure what you think is 1,000', or 304.8 meters, but it is actually 999' or 304.45 meters. Appears that you have measured correctly, but without pulling the tape a second pass, you may make a mistake.

Duane, You are absolutely correct. Reading the tape on the metric and imperial sides may help catch errors in reading the tape. It won't catch errors due an end moving or slipping from the tire, or if the vinyl tape moved. Measuring forward and then repeating by measuring backward will help catch most of the tape measurement errors. -- Justin

But how do you hold the other end where there is nothing but nylon clad steel tape to grab onto?  After I asked the question I tried this and it seems to work OK at up to 24 pounds of pull. Cut 2 pieces of 1 1/4" flat stock (one 1 3/4" long and the other 3 " long). Bolt them together with 3/16" machine screws and nuts.  Drill a 3/8" hole at the far end of the 3" piece.   Lot of other better materials but that is what I had.

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OK, I pulled the reel cover plate and there is a loop of pure tape but to make that loop the tape necked down to about half.   Pretty sure though that the loop would deform plastically with a direct hook up to the thin metal De-Liar hook.   You could pretty easily rig up a clevis arrangement though and use the loop.  I have been "calibrating" my hand with a 20 pound weight just before measuring and directly pulling on the tape.

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