LLBing: the most harmful form of MFFY

>From: Scott en Aztlán
>Date: 12/22/2004 2:39 P.M. Central Standard Time
>Message-id: >
>
>On 22 Dec 2004 02:11:18 GMT, Jim Yanik .> wrote:
>
>>> Since cosine error can only cause the radar to read low, it's not
>>> really important. The charge is the same regardless, and the radar
>>> reading is still good evidence (ignoring other sources of error,
>>> anyway -- the biggest being targeting the wrong vehicle) that you're
>>> doing _at least_ the speed on the readout. If they were trying to
>>> enforce minimums with radar it would be a different story.
>>
>>Courts seem to take accuracy of evidence into consideration.(usually)
>>As I noted,having the wrong TIME or date on the ticket is grounds for
>>dismissal.
>>
>>Inaccurate evidence should be useless legal evidence.
>
>Almost all radar gun readings are going to have some cosine error -

"Almost all?" They all will unless they can curve the beam :-)

>the cop would have to be standing in the middle of the road and aim
>completely orthogonally to your car in order to completely eliminate
>it. If the courts refused to accept the reading on the gun as a
>scientifically valid lower bound on the vehicle's speed measurement,
>municipal revenue enhancement activities all over the country would
>grind to a screeching halt.
>
>--
>Sloth Kills!
>http://www.geocities.com/slothkills/
>
>

All that's really necessary to get an accurate reading is to calibrate the guns
every so often, I imagine. I don't have any experience with them personally
though so maybe a police officer would be the best source of info on their
reliability.

Anyway..

Cosine error is really, really tiny in pretty much any real situation.

A radar gun 20 feet off to the side of the vehicle's path while the measured
car is only 100 feet down the road (just over one second away at 60 mph) would
only produce a 2% error in the reading (assuming it was calibrated of course).
All that would mean is if you were going 75mph, the gun would read 0.9798 *
75mph = 73.5mph (would show up as 74mph on the gun).. This is if the officer
whips out the gun and tags you only one second before you pass him while
parked, most likely, clear off the side of the road. Roughly one second
earlier it would read 74.6 mph (rounded to 75mph, the real speed anyway.)

Don't ever use cosine error to argue this because the only thing that it could
ever show is that you were travelling faster than the gun read :-)

Todd Wasson
Racing Software
http://PerformanceSimulations.com
http://performancesimulations.com/scnshot4.htm