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Purpose of the SCPF

pastmemberpastmemberMember
Quote from the Blane Bachelor article on course measurement in Runner's World, posted here by Justin Kuo:

"There’s the Short Course Prevention Factor to figure in, too. According to USATF and the International Association of Athletics Federations, all races must be measured one-tenth of one percent of the total distance long, which ensures that the course cannot possibly be found to come up short in case of a record."

Well, leaving out Blane's statement "...cannot possibly be found to come up short in case of a record.", which is not true, I have understood that the purpose of the SCPF is to compensate for known and unknown reasons that any particular calibrated JOC measurement may vary from a (theoretical) equivalent steel tape measurement. "Known" being greater wobble during measurement than during calibration, "unknown" being a difference between tangents measured and tangents run in the corresponding race.

The article would seem to me to inform the layperson that we add in this random extra distance to account for the "unknowns", so that we have a small "fudge factor" in the event of a record and subsequent validation. I am sure that there must be a lot of material on this subject in our archives. I have not read it. But I was taught that measurement rides are often or typically subject to more wobble than calibration rides. I certainly agree with this. My cal rides are typically on quiet streets with no stopping and no guessing tangents. There is little or no distracting traffic on these cal rides, so wobble is at a minimum. Not so for me during certification rides, especially when there is traffic around. I am sure I am wobbling slightly more during measurement, and I know that wobble can add up and can contribute to any given measurement being short of the stated distance.

Maybe I am misinformed. I haven't read the rulebook that Dave Katz referred to about this.
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AdminAdminMember
Lyman,

The rule David is referring to says the SCPF is "recommended" to prevent the course from turning up short on re-measurement. So what Blane says basically reflects what the rule says (although like you I would have said "unlikely to" rather than "not possible to").

I don't know that we should read more into the SCPF than is really there. Just a mechanism to avoid verification failures. If the USATF/IAAF record rule was that the course couldn't be more than 0.1% short, I doubt we'd be using an SCPF.
pastmemberpastmemberMember
Thanks for this explanation, Mark.

To me, this still begs either the question "what causes potential verification failures that requires us to add 0.1% to our measurements"? - or, if a certified course produces a record, and the the course is run as certified, why add 5.28 feet per mile"? For a marathon, we are adding 138+ feet to the course with the SCPF.

Not challenging this rule, or the reasoning behind it. Just interested in the philosophy/rationale behind it.
genenewmangenenewmanRRTC Chairman
The reason for the rule is no one can measure say 5000 meters exactly. I remember a time when the SCPF wasn't used and the switch was made to include it for our measurements. I recall one of our long time Certifiers resigning. He stated we are not using "REAL NUMBERS".

If you google the history of the SCPF, You will find several interesting articles. One is posted on our BB.

This rule is used as a safety factor.
B bobthurstonMember
I was going to jump in earlier, now I see that Mark and Gene have said a lot of what I wanted to say. The SCPF is there in recognition that competent measurers, using the calibrated bicycle method, will get a range of results. We add 0.1% to ensure that all (or almost all) of the courses we measure are NOT SHORT, and reports over the years have confirmed that it's working.

As Mark said, we can't read too much into it; the variation may have many causes but the SCPF is there to prevent the course from being short, or from being found short. It's worth remembering that ALL measurements are like this-- their accuracy is defined as a range, not a specific point.

Gene's point is so important, especially in discussions with folks who don't do measuring: we're NOT adding 138 feet to what we KNOW to be a marathon distance-- we are adding 138 feet to WHAT WE MEASURED as a marathon distance-- this so that the expert measurer who will possibly check our course will not find it short.
pastmemberpastmemberMember
Good point, Gene. Good explanation, Bob. I appreciate this.

I have done only one validation measurement. It was for a 12K where pending records had been set. My measurement, without the SCPF, of course, came within a few inches of 12K. If my measurement was accurate, the certified course was about 39 feet long. Not a big deal, I suppose.

This course was certified by one of the most meticulous measurers I know of. I would bet that most courses he has measured would validate with equal accuracy. Until a marathon he measured experiences something like the leader tripping, falling, and being passed in the final 138 feet, though, I agree no one should read too much into it Smiler .
duanerussellduanerussellMeasurer
Bob, it could have been a few inches long, and still be "within a few inches of 12k".

Lymon, you verified, not validated.

We add the SCPF so we have room for the swerves, wobbles, and pursuing dogs. We don't add 138' to a marathon course. We add 138' to our desired 42.195 km (Bob Baumel, don't you love us using metric and feet/inches in the same sentence???) measured distance, knowing that we can't ride a perfect course. If we taped it after the bike measurement, it would always be less than 42.195 meters longer than 42.195 km. To say a marathon course is 42.195 meters long is not accurate. It is (most likely) longer than 42.195 km, but always less than 42.237 km (length with SCPF).
AdminAdminMember
We have our rules and procedures in place so that a 5km course certified in California and a 5km course in Virginia are very close to the same length. If a guy in Virginia breaks an American record set by a guy in California, the important thing is that they both ran very close to the same distance. It's really not that important whether they both ran closer to 5005 meters or closer to 5000 meters, as long as they both ran very close to the same distance.

If you're going to bemoan the fact that we measure courses to be 5005 meters, you should also bemoan the fact that a "5000" run on the track is actually only 4978 meters long. Measuring 30cm from the curb is the definition of what a 5000-meter course IS on the track. Measuring the course to 5005 meters (and also measuring 30cm from curbs) is the definition of what a 5000-meter course IS on the roads.
mikewickiser 2mikewickiser 2Member
I don't want open a can of worms but the SCPF protects the course in the event of a Verification. In the US anyone can measure a course and work with their state certifier to obtain a certified course.
Should a record worthy performance be achieved it is common to send a professional level measurer to ride the course. Those measurers are almost always IAAF A or B measurers.
I always knew that the marathons I ran were theoretically 42+ meters long and I really wished the course was shorter but I also knew that we are all human and the standard for all IAAF and USATF certified courses includes the .01% SCPF.
It doesn't happen often but over the years a few courses have come up short upon Verification measurement.
pastmemberpastmemberMember
Bob, of course the validation of the course I did was "within inches". I am stating that the verification/validation I performed, without the SCPF, revealed that 12K on my counter arrived nearly exactly 12 meters SHORT of the actual race Finish line. If my measurement was good, this course (a 12K) was theoretically 12 meters long. Of course, I measured to the Finish line, which came out to 12,012 meters plus a few inches.

See? Even though we understand these concepts, they aren't easy to explain to the layperson.

I am not grasping your "skin of the teeth" thing. I don't think you are saying that a validation measurement should come up longer than the stated distance without the SCPF - right?

Duane, Bob: you seem to be using "validation" and "verification" interchangeably. Help me understand the difference.
Last edited by pastmember
pastmemberpastmemberMember
Mark, thanks. This confirms what I thought. Of course, I am not bemoaning anything. But I have talked to competitive runners in my region who do. In my conversations, many of them seem to think they are always running longer than the stated distance, even though some of them are savvy enough to run all the tangents.

Because I conduct and time races, I want to have all my ducks lined up when athletes question me about the race distance. GPS device wearers are one class of questioners. I am prepared to handle any questions from them. I want to be able to authoritatively and concisely explain what is really happening with certification measurements to competitive athletes when they ask. This discussion is helping me get there. Thanks.
B bobthurstonMember
quote:
My measurement, without the SCPF, of course, came within a few inches of 12K.

--This one seems to say that you found the course as laid out to be within inches of 12,000 meters, so that is definitely by the skin of its teeth, a little tighter measurement would have found it to be short.

quote:
I am stating that the verification/validation I performed, without the SCPF, revealed that 12K on my counter arrived nearly exactly 12 meters SHORT of the actual race Finish line. If my measurement was good, this course (a 12K) was theoretically 12 meters long. Of course, I measured to the Finish line, which came out to 12,012 meters plus a few inches.

--This later quote is more in line with what you told me at the time, which is that there were indeed about 12 meters of "cushion" in the course, according to your verification measurement.

Some things an elite runner might need to think about:
-- This is the way road course length is established. Any "extra" distance they run is a very small price to pay for the ability to set records or compare times in road races-- neither of which was permitted before course certification was established.
-- We don't know for sure if the course had "extra" length in it
-- Even if we assume it is longer than the stated length, it is a very small amount both absolutely and relatively. If someone can run 12K in 30 minutes, they are running about 6.7 meters per second, and the 12 m of SCPF costs them less than 2 seconds. Probably less than they might lose through -- you name it, imperfect following of spr, lack of good drafting, getting squeezed in a crowd, etc.

I'll stop, I just mainly wanted to explain the "skin of its teeth comment.

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