how can i prove my speedometer is not off?

[Captain Awesome]

Originally Posted by Steve Dallas

Really? REALLY???? No one posts the most obvious and easist way to do this?

GPS? That has a little built in inaccuracy for civilians. I've seen mine vary by 2-4mph when I'm on cruise control. The altitude is off by quite a bit as well.

Either no one remembers the old-school way of doing this...or are just lazy these days. You know that most highways have mile markers. If you set your cruise control at 60 (hopefully level road, though not absolutely necessary), and start your stopwatch as you pass the mile marker. When you pass the next one, you stop it. If you did one mile in one minute, then you are doing 60mph. Simple. Accurate.

That's what I would suggest.

It's not only "old school".... it's the best way to do it.

[oldfriend]

Originally Posted by justin2fast4u

me and this girl from work have been driving down the highway together every night after work and i will tell her dang your driving fast, like 80 and she is like no i never went over 70

then tonight we tested it, she said go 60, so i set my cruise to 60 and she did the same

she left me, so im pretty sure her speedometer is wrong, or im worried it could be mine? how can i prove it?

She is just trying to tell you, TRY2CATCHME

[evilbeef54]

Originally Posted by Steve Dallas

Really? REALLY???? No one posts the most obvious and easist way to do this?

GPS? That has a little built in inaccuracy for civilians. I've seen mine vary by 2-4mph when I'm on cruise control. The altitude is off by quite a bit as well.

Either no one remembers the old-school way of doing this...or are just lazy these days. You know that most highways have mile markers. If you set your cruise control at 60 (hopefully level road, though not absolutely necessary), and start your stopwatch as you pass the mile marker. When you pass the next one, you stop it. If you did one mile in one minute, then you are doing 60mph. Simple. Accurate.

of course you are assuming that the amazing, perfect, well adjusted city worker managed to poke his head out from his whiskey fueled attempt at life long enough to accurately measure 5280' and drop a mile marker there... the same guy that couldn't manage to load the reflective bumps correctly so everyonce in a while you see a red flash when driving down the road because he installed a marker backwards....

but yeah this is probably the easiest and most accurate way to go, obviously longer distances measured = more accurate readings...

[xXSilencerXx]

Originally Posted by Steve Dallas

Really? REALLY???? No one posts the most obvious and easist way to do this?

GPS? That has a little built in inaccuracy for civilians. I've seen mine vary by 2-4mph when I'm on cruise control. The altitude is off by quite a bit as well.

Either no one remembers the old-school way of doing this...or are just lazy these days. You know that most highways have mile markers. If you set your cruise control at 60 (hopefully level road, though not absolutely necessary), and start your stopwatch as you pass the mile marker. When you pass the next one, you stop it. If you did one mile in one minute, then you are doing 60mph. Simple. Accurate.

Not so much as built in inaccuracy so much as limitations within the device. For example I built a HUD for a motorcycle helmet with a GPS for a senior design project, and since I was able to use a larger antenna I got spot on results.

That said, the mile marker way is stupid easy and simple to do.

[FightingScallion]

Originally Posted by Steve Dallas

...

GPS? That has a little built in inaccuracy for civilians. I've seen mine vary by 2-4mph when I'm on cruise control. The altitude is off by quite a bit as well.

...

The civilian GPS dither for the Navstar constellation was removed by the Clinton administration (Executive order issued in 1996, achieved May 2000). Accuracies from Navstar are probably on the order of a few centimeters (distance in any direction) and 10 nanoseconds if you have at least 4 satellites (more satellites is better, but you need an absolute minimum of 4, whereas 5 or more will give you a fantastic clock correction). Your biggest source of inaccuracy may come from signals going through the ionosphere.

Additionally, an increasing number of GPS devices can use GLONASS, Galileo (usually just planned compatibility, since that one isn't IOC yet), and some use Beidou.

The accuracy from these is very good. You're looking at +/- 1 mph max, I'd say. Based on just tire pressure variations, you've probably got that built into your vehicle.

[nitrorcr1787]

Originally Posted by Comrando

Use your trip odometer and compare it to the mile marker signs on the highways.

The longer the distance the more accurate.

Took the words out of my mouth. Get on a road with mile markers, set the cruise to 60 and you should cover a mile in 60 Sec.

[boltmark]

Originally Posted by cyberLS

fly by a cop and see what he clocks you at?

[hightower]

Originally Posted by justin2fast4u

but she also drove a truck one night and swears she wasn't driving over the speed limit when she clearly was, so thats 2 different cars, i doubt they are both messed up

Trucks feel slowed cause you're higher off the ground and it looks like you're not traveling as fast. Before my camaro I drove a truck. And I borrowed my sisters 2004 volvo S40 for 3 weeks in a row. Switched back to my truck and every time I went for a drive I noticed I was doing 10MPH over what I normally did, just because it felt like I was going slower.

Originally Posted by stieger

maybe I'm the only one who thought of this, but who's to say she isn't just screwing with you?

[spectre_]

Originally Posted by stieger

maybe I'm the only one who thought of this, but who's to say she isn't just screwing with you?

We have a winner!!!!!

[austinjames]

gps

[bumblebeecamaro]

I'm surprised no one has asked this, but.................... what does she look like? lol

[matthook]

Originally Posted by stieger

maybe I'm the only one who thought of this, but who's to say she isn't just screwing with you?

+1

[matthook]

Originally Posted by bumblebeecamaro

I'm surprised no one has asked this, but.................... what does she look like? lol

+2 hahaha

[Rangore]

Originally Posted by Steve Dallas

Really? REALLY???? No one posts the most obvious and easist way to do this?

GPS? That has a little built in inaccuracy for civilians. I've seen mine vary by 2-4mph when I'm on cruise control. The altitude is off by quite a bit as well.

Either no one remembers the old-school way of doing this...or are just lazy these days. You know that most highways have mile markers. If you set your cruise control at 60 (hopefully level road, though not absolutely necessary), and start your stopwatch as you pass the mile marker. When you pass the next one, you stop it. If you did one mile in one minute, then you are doing 60mph. Simple. Accurate.

^^^ this^^^

Originally Posted by stieger

maybe I'm the only one who thought of this, but who's to say she isn't just screwing with you?

^^^ and this ^^^
She likes you and it's the only way she knows how to keep you talking to her.