How exactly is a "measured mile" measured?

[Elmo Rodge]

OK Tony. So how do you lay out the 1.3 mile course at El Mirage?    Wayno

[dw230]

How long have we been using 1.1 miles at El Mirage? Do we have to toss all the records set since that date?

DW

[F104A]

The accuracy of time is 20 nS (.000000002 seconds), So we can discount that error.

The accuracy of position is within 3 mm, regardless of distance. For two points that increases to 6mm, or .23622 inches, or +/- 0.000001864 miles.  This includes any change in altitude too (which traditional systems don't do)

200 mph is 1 mile per .005 hour

1.000001864 miles / .005 hour is 200.000372 miles per hour

0.999998135 miles / .005 hour is 199.999627 miles per hour

so the answer is +/- 0.000372 miles per hour

800 mph is 1 mile per .00125 hour

1.000001864 miles / .00125 hour or +/- 0.00149 mph accuracy at 800 mph.

[fredvance]

Thanks Ed. I think!

[Stan Back]

Wow!

I'm feeling great!  We're nearly breaking records set at 1.3 miles.  Another 1056 feet and we'd be there.

[Elmo Rodge]

We've been NHRA'd.  Wayno

[Jack Gifford]

Umm... what was F104A describing?

[jacksoni]

Umm... what was F104A describing?

I think GPS accuracy.

[jacksoni]

The accuracy of time is 20 nS (.000000002 seconds), So we can discount that error.

The accuracy of position is within 3 mm, regardless of distance. For two points that increases to 6mm, or .23622 inches, or +/- 0.000001864 miles.  This includes any change in altitude too (which traditional systems don't do)

200 mph is 1 mile per .005 hour

1.000001864 miles / .005 hour is 200.000372 miles per hour

0.999998135 miles / .005 hour is 199.999627 miles per hour

so the answer is +/- 0.000372 miles per hour

800 mph is 1 mile per .00125 hour

1.000001864 miles / .00125 hour or +/- 0.00149 mph accuracy at 800 mph.

Yes, but as everyone will say there is a big Acura difference between 199.999627 and 200.000372.

[Sumner]

...Yes, but as everyone will say there is a big Acura difference between 199.999627 .....

...if I had only done this.....

........ and 200.000372......

... a big smile and a vist with Dan  ,

Sumner

[Malcolm UK]

A record is not measured to 0.001 mph.  Although record speeds are reported to three decimal places.  The measured parameter is time, which may be recorded to many decimal places but is then truncated to 3dp for (FIA) record purposes.

Hmm . . .
So if you're timed at 7.2009 for the mile, which figures to 499.9375 mph, you'd be credited as going 500.

Yep.  It needs someone smarter than me to explain why this is considered to be the "correct" way to do the calculation.

Not sure if the rule book helps, but the FIA rules follow. At no time could 499.9375 be anything greater than 499.937.

FIA D12.3.2 Time accuracy. Record time with an accuracy of 1/1,000th of a second and calculate the mean time with an accuracy of 1/1,000th of a second with no rounding off.

FIA D12.3.3 Speed Accuracy. Calculate and record speed with an accuracy of 1/1,000th of mph or kph

FIA D12.3.4 Conversion. Convert speed thus calculated to kph or mph with no rounding off using the defined conversion factor.

FIA D12.3.5 Precision. If the timekeeping equipment has accuracy greater than 1/1,000th of a second, its precision shall be set to record times to 1/1,000th of a second with no rounding off to allow direct use of all readings.

[TrickyDicky]

A record is not measured to 0.001 mph.  Although record speeds are reported to three decimal places.  The measured parameter is time, which may be recorded to many decimal places but is then truncated to 3dp for (FIA) record purposes.

Hmm . . .
So if you're timed at 7.2009 for the mile, which figures to 499.9375 mph, you'd be credited as going 500.

Yep.  It needs someone smarter than me to explain why this is considered to be the "correct" way to do the calculation.

Not sure if the rule book helps, but the FIA rules follow. At no time could 499.9375 be anything greater than 499.937.

FIA D12.3.2 Time accuracy. Record time with an accuracy of 1/1,000th of a second and calculate the mean time with an accuracy of 1/1,000th of a second with no rounding off.

FIA D12.3.3 Speed Accuracy. Calculate and record speed with an accuracy of 1/1,000th of mph or kph

FIA D12.3.4 Conversion. Convert speed thus calculated to kph or mph with no rounding off using the defined conversion factor.

FIA D12.3.5 Precision. If the timekeeping equipment has accuracy greater than 1/1,000th of a second, its precision shall be set to record times to 1/1,000th of a second with no rounding off to allow direct use of all readings.

Malcolm, I think tortoise's point was that if you apply the above rules then 7.2009 rounded off becomes 7.200 and, hey presto, 500 mph.

[PorkPie]

...Yes, but as everyone will say there is a big Acura difference between 199.999627 .....

...if I had only done this.....

........ and 200.000372......

... a big smile and a vist with Dan  ,

Sumner

Sumner,

I think you taking about the very exclusive 199,5+ mph club at the salt....for a short time I was also a member of this club.....but may be they ask Betty Burkland...she had this experience for 15 years....she run 199,997 mph.....before finally she could get her red hat....

[Malcolm UK]

Malcolm, I think tortoise's point was that if you apply the above rules then 7.2009 rounded off becomes 7.200 and, hey presto, 500 mph.

The figure of 7.2009 is never 'seen' by the FIA timekeeper as the rules are written. The fourth decimal place is just ignored.

Not sure how you could ever arrive at the average or mean time being 7.2009.

[tortoise]

. . . The fourth decimal place is just ignored.

Nonetheless, our notional vehicle is actually going less than 500 mph, but is credited with that speed.  Not a big deal, just a curiosity.