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Course Measurement and Certification Procedures

Laying Out a Calibration Course

Accuracy of the calibration course is vital since any error will be multiplied when it is used for measuring a race course. A calibration course must be on a straight, paved, reasonably level, and lightly traveled stretch of road, and must be at least 300 meters in length. Accuracy is also generally best if you can minimize the time required to transport your bike between the calibration course and race course. Therefore, you should consider laying out a calibration course close to the race course to be measured, especially when you must travel a long distance to reach the race course site.

Method of Measurement: The standard method of measuring a calibration course is to use a steel tape. Any steel tape, either surveyor's style or construction style, may be used, but to be confident of accuracy, get a tape made by one of the better-known manufacturers of surveying or construction equipment. Nylon-clad steel tapes are okay, but fiberglass tapes are definitely not acceptable. Electronic Distance Meters (EDM) can achieve greater accuracy than steel tapes, although that extra accuracy is not really needed for calibration courses used in the bicycle method.

Siting your Calibration Course: Choose a location that will be safe and convenient for calibrating a bicycle. Every time you measure a race course, you'll need to ride the calibration course at least eight times (four before and four after), and you'll want to ride it in both directions. Calibration courses are usually measured along the edge of a straight road—the same distance from the edge as you would ride your bike. (But on a street where vehicles may park, you may wish to measure far enough from the edge to avoid any parked vehicles.)

The marks defining the endpoints of your calibration course must be in the roadway where your bike wheel can touch them—not off to the side somewhere. In general, endpoints should be marked by nails driven into the road. Urban areas, however, often have numerous permanent objects in the street (sewers, manholes, etc.) that may serve as one or both endpoints of a calibration course.

Your calibration course will be most resistant to getting obliterated when the road is resurfaced if both endpoints are permanent objects such as sewers or manholes, etc. In this case, you'll have an odd-distance calibration course such as 324.54 meters—which is perfectly acceptable. You can also make your calibration course an even distance, where both endpoints are close to permanent landmarks, and where you've precisely located both endpoints relative to such landmarks.

When laying out an on-site calibration course that you will probably use only once, survivability of the calibration course is unimportant, and convenience is paramount. So just lay out a whole number of tape lengths; for example, 10 lengths of a 30-meter tape or 12 lengths of a 25-meter tape (laid out distance = 300 meters), or 10 lengths of a 100-foot tape (laid out distance = 1000 feet = 304.8 meters).

Certifying your Calibration Course: You are not required to submit a map for every calibration course you measure. However, when you lay out a calibration course that you think you'll want to use again in the future, or one that you think other measurers would like to use, you may draw a map for it, and you will be issued a certificate that will simplify future use of the calibration course.

Whether or not you want such a certificate, you must submit an "Application for Certification of Calibration Course" form, along with all your measurement data (including the "Steel Taping Data Sheet" if course is measured by steel tape), whenever you lay out a new calibration course.

If you don't submit a map with your application for calibration course certification, then this calibration course, if approved, will be considered certified for only that one measuring occasion. If you want to re-use the calibration course on a later occasion, you must resubmit all the paperwork for the calibration course.

If you do submit a map for the calibration course, and are issued a certificate for it, then whenever you (or others) want to re-use this course, you need only submit a copy of the certificate/map.

If you draw a calibration course map, it must describe the endpoint positions as precisely as possible. Ideally, the endpoints should be permanent objects in the street (such as sewers or manholes), or should be referenced to such objects so precisely that you could relocate your endpoints to an accuracy of one centimeter in case the road is resurfaced and your markings obliterated. If you can't describe the positions that precisely, then the certification will be considered to expire when the road is resurfaced.
 

Measuring Your Calibration Course With a Steel Tape

Equipment Needed for Taping: A steel tape, preferably at least 25 meters in length; masking tape and ballpoint pen for marking tape lengths on the road; a thermometer for checking pavement temperature; possibly a spring balance for checking tape tension; Notebook and copies of the "Steel Taping Data Sheet" for recording data. You can tape a calibration course with just two people, but it might go more smoothly with a third person (for example, to watch for traffic and take notes).

Requirements: You must tape the course at least twice. (Normally, the second measurement will be done in the reverse direction from the first.) Use a new set of intermediate taping points (new pieces of masking tape) for the second measurement. But treat the second measurement as a check of the distance between the same endpoints you measured between the first time. Thus, the second measurement should result in a number indicating the distance between your original endpoints (not in a new set of endpoints).

Your final result will be based on the average of both measurements, corrected for temperature (see below). If desired, you may then adjust the course to obtain a desired even distance (such as 1 km).

Basic Taping Technique:

For each tape length, the Lead and Rear tapepersons first shake out the tape until it lies straight and flat on the road. The Rear tapeperson sights ahead to keep the Lead tapeperson properly aligned or the Lead tapeperson uses a ruler to maintain constant distance from the road edge or other desired (straight) line.

Intermediate taping points are marked with ballpoint pen on masking tape. After stretching the tape to its approximate position, the Lead tapeperson sticks a piece of masking tape on the road, covering the position where the mark will be made. The Lead tapeperson then starts pulling on the tape with proper force (see below). When the Rear tapeperson has his endpoint firmly positioned over the mark (with the tape under tension), he shouts "mark." At this signal, the Lead tapeperson draws a fine line on the masking tape to mark the exact endpoint.

Long steel tapes are always designed so that the tape may be easily detached from the reel. You'll find that taping is easiest if you do this, and don't carry the reel along with you!

Don't panic if you see that a car is about to ride over your tape. If the Lead and Rear tapepersons hold the tape flat and firmly against the road, it will probably come out okay. (But a twisted tape will likely get broken.)

When walking from one taping position to the next, only the Lead tapeperson holds onto the tape, which is allowed to drag freely on the road. (If Lead and Rear tapepersons attempt to hold both ends off the ground, it may drag at a spot in the middle, resulting in one extremely worn area!)

Counting the Tape Lengths:

Miscounting the tape lengths in a calibration course is a disaster; the "10 km" race course you lay with it might really be 9 km or 11 km! Fortunately, it's easy to guard against such counting errors.

One handy trick is to pre-number your pieces of masking tape before you tear them off the roll as in the following diagram:

Pre-Numbering the Masking Tape

As pieces of masking tape are used, the Lead tapeperson adds more numbers to the roll, so it always has at least two or three numbered segments that haven't been used yet. (Be sure to write the numbers so they won't be confused with the fine lines that will denote actual tape endpoints.)

After the taping, walk or jog the course to check the tape count. It is also helpful to do a bike check as follows: Ride a bike equipped with Jones Counter over the whole calibration course, and also over any one tape length. The number of counts recorded on the whole course, divided by the number of counts recorded in a single tape length, should come out very close to the number of tape lengths you laid out.

Such a bike check may not be necessary if you will be measuring with a bike that you've previously calibrated on a calibration course that you know to be accurate. Then, if you miscount tape lengths while laying out a new calibration course, you'll see that your riding constant is "way off" as soon as you start calibrating on the new course.

Know Your Tape's True Zero Point:

Many steel tapes (especially construction-style tapes) don't have their zero point on the graduated portion of the tape. Misjudging the tape's zero point is harder to catch than miscounted tape lengths, but the effect can be insidious. For example, if you misjudge the zero point by 3 cm on a 30-meter tape, your measurements can come out short by about 1 meter per kilometer, entirely canceling our "Short Course Prevention Factor." The runners won't notice anything wrong with their times, but if the course ever needs to be verified, it will be found short.

Before using any tape, examine its markings carefully. If zero is not on the graduated portion of the tape, then take a ruler (or another portion of the same tape) and measure to find out where the true zero is. On construction-style tapes, it's usually at the outer edge of a "hook-ring" as in the following diagram.

Construction-Style Hook-Ring

While examining your tape, make sure you also understand all its other markings. Is it a metric or Imperial tape? Metric tapes are often graduated to the millimeter, but you must check whether the numbering between meter marks denotes centimeters or millimeters. Imperial tapes may be graduated in either feet & inches or decimal divisions of a foot. The following diagram shows some common styles of tape graduations:

Styles of Tape Graduations

Note: Drawings of tape graduations taken from Lufkin's online catalog.

Correcting for Temperature:

Steel tapes are manufactured to be accurate at 20 °C (68 °F), but the tape expands when heated and contracts when cooled.

To correct your taped distance for temperature, set out a thermometer on the pavement and shaded from the sun. Read the thermometer before you start taping, and after you finish taping. Find the average temperature, and work out the correction to your raw taped distance by using the formula on the "Steel Taping Data Sheet," or by interpolating in the table below.

While it's a good idea to work out the temperature correction whenever you tape a calibration course, you are required to do so only when it's cooler than 20 °C (68 °F) since, in this case, the true measured distance is shorter than your raw laid-out distance. But note: If you are a certifier doing a Verification measurement, you should always do the temperature correction, regardless of whether it’s warmer or cooler than 20 °C.

The following tables show the temperature correction for a number of temperatures cooler than 20 °C, and for several course lengths. (You may interpolate or extrapolate in the table for other temperatures and course lengths.) Remember: at temperatures cooler than 20 °C, the true measured length is shorter than your raw taped distance (so you'd need to lengthen your course if you want to obtain a desired exact distance). At temperatures warmer than 20 °C, the corrections are in the opposite direction.

I. Corrections in centimeters
     Calibration Course Length
Temp   300 m 500 m 800 m 1000 m

20 °C   0.0 0.0 0.0 0.0
15 °C   1.7 2.9 4.6 5.8
10 °C   3.5 5.8 9.3 11.6
5 °C   5.2 8.7 13.9 17.4
0 °C   7.0 11.6 18.6 23.2
-5 °C   8.7 14.5 23.2 29.0
II. Corrections in inches
     Calibration Course Length
 
Temp
   
1000'
500 m
1640.42'
1/2 mi
2640'
1000 m
3280.84'

68 °F   0.0 0.0 0.0 0.0
60 °F   0.6 1.0 1.6 2.0
50 °F   1.4 2.3 3.7 4.6
40 °F   2.2 3.6 5.7 7.1
30 °F   2.9 4.8 7.8 9.6
20 °F   3.7 6.1 9.8 12.2

How Hard to Stretch the Tape:

Just as steel tapes are manufactured to be most accurate at a particular temperature, they are also most accurate when stretched with a specified amount of force. But while you may not have much control over the temperature at which you do the measurement, you can adjust the force you apply to the tape to match the correct force for your tape. (Unfortunately, the proper force varies from tape to tape.)

You can find out how hard you are stretching the tape by using a spring balance as in the following diagram:

Stretching Tape with a Spring Balance

You needn't actually use a spring balance this way while taping your calibration course; it is enough to do a few trials beforehand to get a feel for the correct tension. With a little experience, it will be easy to judge the proper force, and you'll be able to dispense with the spring balance entirely. Note: It is acceptable to answer question 17 on the "Application for Certification of Calibration Course" by saying you estimated the tension "by feel."

Also, since the errors due to slight variations in applied force tend to be very small, the spring balance you use for checking tape tension needn't be a precision instrument. The type sold in sporting goods stores for weighing fish is quite adequate!

The correct force for stretching a particular tape is sometimes embossed on its blade near the zero end. For example, if you find the markings "20 °C, 70 N" it means that the tape was designed to be accurate at a temperature of 20 °C and tension of 70 newtons (approximately 7 kilograms-force or 16 pounds-force). If you can't find any markings of this sort, use a value from the following table. The first entry in this table (for metric tapes) seems to be emerging as an international standard, so is generally a safe choice if you're not sure which one to pick.

Standard Tension for Various Steel Tapes

Std. Metric tapes (30 m, 50 m, etc.):     50 N ≈ 5.0 kgf ≈ 11 lbf
Traditional U.S. 100 ft tapes:     45 N ≈ 4.5 kgf ≈ 10 lbf
Heavy-gauge steel U.S. 200 ft tapes:     90 N ≈ 9.0 kgf ≈ 20 lbf
   N = newton, the modernized metric (SI) unit of force.
   kgf = kilogram-force, an older (obsolete) metric unit of force.
   lbf = pound-force, the unit of force in the Imperial system.

One mistake people sometimes make is to pull with less force when using a smaller portion of the tape. For example, if a 50 m tape requires a tension of 50 N, they might apply a force of only 25 N when measuring a 25 m distance because only half of the tape is used. That is a fallacy! The correct tension is independent of the length of tape used. If a tape requires a tension of 50 N, you must pull with a force of 50 N, regardless of how much or how little of the tape you are using.


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