SCPF using a steel tape

From the Measurement Manual, "Because it is difficult to follow the shortest possible route perfectly, an extra length factor
of 0.1%, called the short course prevention factor, is incorporated into the calibration
procedure. Use of the factor ensures that your course will not be short, even if you make
small errors in following the shortest possible route."

Since this course wasn't measured by riding, I would not use the SCPF.

I would still add the SCPF. If you measure it to be 500 meters with no SCPF, then the person who comes later to verify the course has a 50% chance of getting a measurement that is longer than yours, and a 50% chance of getting a measurement that is shorter than yours(failed!!).
If you are measuring and also verifying, I would not add the SCPF.

I measured a track with two steel tapes. I used 0.03% SCPF to cover tape calibration error and measuring error. Here is a bit from my report. Sorry about poor formatting after I copied and pasted.

Harrow School Track Marathon Measurement – 7 DEC 2012
The length of this 400m track has not been certified by UKA or IAAF. Therefore the length was measured using two
class II steel tapes. The tape could be guided around the track by placing it against the plastic kerb on the inside of
lane 1. The tapes were tensioned at 10 lbs using a spring scale at the 50 m end. The zero end was held against the left
edge of sticky tape placed on the side of the kerb. For the first lap sticky tape was placed exactly at the 50m points. For
the second measurement with the second tape the tape zero was again placed against the left tape edge and the scale
reading was then taken opposite the left edge of the sticky tape near 50m.
Roles: First tape measurement: Tape zero - Geoffrey Sandford, Tape 50m & note recording - Mike Sandford, Tape
tensioning – Steve Paull
Roles: Second tape measurement: Tape zero – Steve Paull, Tape 50m & note recording - Mike Sandford, Tape
tensioning – Geoffrey Sandford
The temperature was 3c before starting and 5C after finishing. Initially it was overcast but weak low sun emerged
during the measurement so the tape 1 measurement was corrected to 3.5C and the tape 2 measurement was
corrected to 4.5C. These values are unlikely to be in error by more than 1C which produce change of correction to the
400m lap length of only 4.4mm
Tape 1
Length 1 50.000
Length 2 50.000
Length 3 50.000
Length 4 50.000
Length 5 50.000
Length 6 50.000
Length 7 50.000
Length 8 48.153

Total for 1 lap 398.153 metres
Correct for temperature, 3.5C tape 1, 4.5C tape 2 : 398.081 metres
add 2pi*300mm for running line at 300mm from kerb : 399.966 metres



Tape 2
50.001 metres
50.003 metres
50.001 metres
50.004 metres
50.004 metres
49.991 metres
49.990 metres
48.157 metres
total for tape2 398.151 metres
temp corrected tap2 398.083 metres
add 2pi*300mm for running line at 300mm from kerb :399.968 metres

AVERAGE OF TWO TAPES
399.967 metres
The result of the tape measurement is 33mm less than 400m. However tape
measurements are less accurate than can be carried out by a surveyor with access
to the centre points of the semicircular arcs and using Total Station measuring
device. We need to apply a short course prevention factor to our tape
measurements in order to guarantee that the marathon course will not be short

Apply Short Course Prevention Factor of -0.03%. This is based on the 0.02%
accuracy of the markings on a class II tape plus 0.01% to cover taping errors. :399.847 metres
Length of marathon: 42195 metres
Number of laps for marathon: 105.5279 laps

So Marathon is 105 full laps + one half lap + 0.0279 of a lap which is 11.15 metres

If track had been surveyed and certified to UKA/ IAAF standards for a track then the
track length would be guaranteed to be between 400m and 400.04m. So in this case
to guarantee at least a marathon distance 105 laps + half lap less 5 metres would
have been required
Therefore our tape measurement results in adding 16.15 metres compared to what
would be needed if the track had a proper UKA/IAAF track survey certificate.

I feel the best way to handle this is with the calibrated bike on this type of course. This way you don't have to do a temperature correction factor and add the SCPF after all is done.

This brings up an even bigger question - should we allow the Certification of a closed loop 1km or 2km course by steel tape alone? the IAAF is now using a 1 km loops for the World Championships and Olympic Games race walk competitions. It would be easier in some situations to just steel tape the entire course. I do not see any problem with this. And I would incorporate the SCPF.

Not sure about if this fit in with David's "bigger question", but long ago I helped a survey team measure an XC course with a 100 meter steel aircraft cable. Looking at survey suppliers today I notice they now use fiberglass tape that claims to not stretch or shrink. That would seem to be a good method for these short loop courses if proved to be accurate. Anyone have any knowledge of them and if they would be acceptable if accurate?

Interesting discussion. On measuring with a cable, I know that this was the preferred method in Japan at one time and I don't know if they still use that method. To measure a marathon they had two 100 meter cables calibrated and used them in a leapfrog fashion with a virtual army of students assigned such jobs as giving line, recording the number of tape lengths, pulling to the correct tension, holding poles at a 30 cm distance from the curb at corners, etc. I can't remember what their SPCF was, or whether they considered that unnecessary.

The question of SCPF when measuring with steel tape is a puzzler. It's reasonable, you would think, that it could be safely set at something less than 0.1%, but I'm not quite ready to agree with 0.03% per Mike Sandford-- mainly because I can think of so many sources of error with steel taping: keeping a good line; inaccuracy and variability of thermometers; the tapes themselves (do we know for sure that a given tape is accurate within 0.02%?)

Right now this is guesswork because we don't have very much data, but maybe someone can think of a way to gather enough information to determine a reasonable spcf for tape measurement.

Thanks to Mike for sharing that track measurement!

Good points IMO, Bob. Remember Dave Katz taking his steel tape for the Olympic Marathon to NIST for calibration? And It was almost an inch short?

This alone seems justification for including a SCPF.

A few years ago I purchased two 50 m "class 1" steel tapes from the Japanese Athletics Federation. The tapes are calibrated every meter!
They shine like a Rolex. I bought two: one to use and the other to keep on the shelf like a piece of fine art!
It will be used (for the second time) in July when we do the official measurement for the Olympic Marathon & RW courses in Rio.

I'm almost afraid to ask, but how much did those super-calibrated steel tapes set you back?

about $800 each
everything is more expensive in Japan

David showed me the tape a couple years ago, while in Boston. It is a work of art!



David's 50 meter steel tape



Calibration certificate for steel tape

Click to see a larger image.

Last year, I purchased a STARRETT certified (NIST traceable) steel tape. The tape included a letter certifying the accuracy.



Click to see a larger image.

The certified steel tape has an accuracy of 0.00833%. Here's the text.

ACCURACY - When the tape is supported on a horizontal surface, and pulled with a tension of 10 pounds at a temperature of 68 degrees Fahrenheit, the overall length will not be in error by more than 2.5mm in 30m or less.