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Reply to "Generic Reply to GPS Accuracy Doubters"

I had RD's call - sounding very worried - after a race, because they had people complaining about their course being long. After talking to way too many of them, trying to explain what I did, I produced a single-page information sheet, "The Course Measurer Says This Is Accurate But My GPS Says..." I began giving this to race directors as part of their cartificate package (certificate, guidance on using the certificate number/map, information sheet, invoice for services).

The sheet, which I've done for 5K, 10K and half-marathon distances, compares RRTC guidance, the answers of a competent course measurer/and the "typical" GPS-using road runner:

- Define "Accurate Course"
CM - USATF/IAAF: "...a course not shorter than the stated distance."
GPS - Varies from person to person

- Define Half-Marathon
CM - 13.10938 miles exactly
GPS - Most say "13.1 miles"

- Number of Unhindered Trips on Course
CM - At least two
GPS - Depends on experience and course knowledge

- Type of Measurement Device
CM - Mechanical (Jones-Oerth)
GPS - Electronic (Consumer-Grade GPS)

- Means of Measurement
CM - Counts per Revolution of Bicycle Wheel
GPS - Triangulated Time to Receive Radio Signal From One-to-Four Satellites

- Degree of Accuracy
CM - +/- 3 inches continuously
GPS - 3m-10m radius 95% of the time, 11m-30+m radius 5% of the time

- Device Ensured Accurate?
CM - Calibration must be done at least twice each measurement day
GPS - Accuracy can be displayed but not controlled

- Comparison Between Trips?
CM - Measurements must be within .08% (55 ft) of each other
GPS - Possible, but not before race day

- Course Travel
CM - Shortest possible distance a runner can legally take on course
GPS - Depends on experience and placing in race

- Start/End of Measurement
CM - Exact start & finish points on course
GPS - Usually with gun/horn, rather than at start line

(EDITORIAL COMMENT: I USUALLY TELL GPS-USERS IF THEY DON'T START AND STOP THEIR UNIT AT THE EXACT START/FINISH LINE ALL THEY HAVE IS A REALLY EXPENSIVE RUNNING WATCH ON THEIR WRIST.)

- Experience Level
CM - 20-year road racer, 6-year measurer, 27 certified courses
GPS - ?

- Oversight
CM - All work approved by certifier/measurer of over 55 active courses
GPS - ?
Last edited by michaelbowen
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