Does anyone know more detail on the accuracy of the laser distance measuring
devices? E.g. something like this:
http://www.stanleytools.com/default....tance+Measurer

It says the accuracy is ± ¼" at 100 feet. Does that scale proportionally, so
that at 50 feet, the accuracy is 1/8", and at 25 feet, the accuracy is
1/16"? Or is the accuracy going to be 1/4" independent of the actual
distance being measured?

Furthermore, is the error a consistent error, or random error? In other
words, if I use it to measure a 100 feet distance 10 times, would I get 10
different readings distributed in a 1/4" range, or would I get the same
reading 10 times that is within 1/4" of 100 feet?

peter wrote:
Does anyone know more detail on the accuracy of the laser distance measuring
devices? E.g. something like this:
http://www.stanleytools.com/default....tance+Measurer

It says the accuracy is ± ¼" at 100 feet. Does that scale proportionally, so
that at 50 feet, the accuracy is 1/8", and at 25 feet, the accuracy is
1/16"? Or is the accuracy going to be 1/4" independent of the actual
distance being measured?

Furthermore, is the error a consistent error, or random error? In other
words, if I use it to measure a 100 feet distance 10 times, would I get 10
different readings distributed in a 1/4" range, or would I get the same
reading 10 times that is within 1/4" of 100 feet?

The surveyor I used told me the law requires a standard accuracy is 0.1'
. A high accuracy measurement gets things to 0.01' .

GPS errors are random. They compute distances by subtracting the
coordinates of the end points. The usual statement people in USAF (who
developed GPS) used to make was "95% of readings will be within 10
meters of the point."

Stubby,

Who the hell said ANYTHING about GPS? Lasers and GPS systems are ENTIRELY
different technologies. Duh!

"Stubby" wrote in message
. ..


peter wrote:
Does anyone know more detail on the accuracy of the laser distance
measuring devices? E.g. something like this:
http://www.stanleytools.com/default....tance+Measurer

It says the accuracy is ± ¼" at 100 feet. Does that scale proportionally,
so that at 50 feet, the accuracy is 1/8", and at 25 feet, the accuracy is
1/16"? Or is the accuracy going to be 1/4" independent of the actual
distance being measured?

Furthermore, is the error a consistent error, or random error? In other
words, if I use it to measure a 100 feet distance 10 times, would I get
10 different readings distributed in a 1/4" range, or would I get the
same reading 10 times that is within 1/4" of 100 feet?
The surveyor I used told me the law requires a standard accuracy is 0.1' .
A high accuracy measurement gets things to 0.01' .

GPS errors are random. They compute distances by subtracting the
coordinates of the end points. The usual statement people in USAF (who
developed GPS) used to make was "95% of readings will be within 10 meters
of the point."

Stubby wrote in
:



peter wrote:
Does anyone know more detail on the accuracy of the laser distance
measuring devices? E.g. something like this:
http://www.stanleytools.com/default....EASURING&TYPE=
PRODUCT&PARTNUMBER=77-910&SDesc=TLM+100+FatMax%26%23153%3B+Tru%2DLaser
%26%23153%3B+Distance+Measurer

It says the accuracy is ± ¼" at 100 feet. Does that scale
proportionally, so that at 50 feet, the accuracy is 1/8", and at 25
feet, the accuracy is 1/16"? Or is the accuracy going to be 1/4"
independent of the actual distance being measured?

Furthermore, is the error a consistent error, or random error? In
other words, if I use it to measure a 100 feet distance 10 times,
would I get 10 different readings distributed in a 1/4" range, or
would I get the same reading 10 times that is within 1/4" of 100
feet?

You would have to ask the manufacturer,as it would depend on what sort of
system they're using to make the measurement;phase shift or Time Of Flight.
It depends on the reference clock crystal's accuracy/stability,and ambient
temperature,for starters.


The surveyor I used told me the law requires a standard accuracy is
0.1'

Maybe for professional equipment,but not for consumer tools.
You get what you pay for.

. A high accuracy measurement gets things to 0.01' .

GPS errors are random. They compute distances by subtracting the
coordinates of the end points. The usual statement people in USAF
(who developed GPS) used to make was "95% of readings will be within
10 meters of the point."


GPS might be used for the measurement reference frequency instead of a
crystal;a much better standard,at higher cost and complexity.



--
Jim Yanik
jyanik
at
kua.net

peter wrote:
Does anyone know more detail on the accuracy of the laser distance measuring
devices? E.g. something like this:
http://www.stanleytools.com/default....tance+Measurer

It says the accuracy is ± ¼" at 100 feet. Does that scale proportionally, so
that at 50 feet, the accuracy is 1/8", and at 25 feet, the accuracy is
1/16"? Or is the accuracy going to be 1/4" independent of the actual
distance being measured?

Furthermore, is the error a consistent error, or random error? In other
words, if I use it to measure a 100 feet distance 10 times, would I get 10
different readings distributed in a 1/4" range, or would I get the same
reading 10 times that is within 1/4" of 100 feet?

As was suggested, the manufacturer would know the answers to these for
sure. It would be easy to set up a test of these questions for
yourself. If your livelihood depends on these answers, you probably
should test it yourself anyway, no matter what the manufacturer says,
or buy a system that exceeds your needed tolerances.

If none of the above is possible, I would venture the following
guesses:
*accuracy does not scale linearly with distance, and the worst case is
not stated
*the error is random

But this is purely based on what I would expect from statements about
accuracy and error in such a tool.

Neil

Finding the keyboard operational
peter entered:

Does anyone know more detail on the accuracy of the laser distance
measuring devices? E.g. something like this:
http://www.stanleytools.com/default....tance+Measurer

It says the accuracy is ± ¼" at 100 feet. Does that scale
proportionally, so that at 50 feet, the accuracy is 1/8", and at 25
feet, the accuracy is 1/16"? Or is the accuracy going to be 1/4"
independent of the actual distance being measured?

Furthermore, is the error a consistent error, or random error? In
other words, if I use it to measure a 100 feet distance 10 times,
would I get 10 different readings distributed in a 1/4" range, or
would I get the same reading 10 times that is within 1/4" of 100 feet?

Being a handheld device, the error is probably for one reading. If you took
10 readings, while holding it in your hand, You will not get 10 readings +/-
..25"
If you mounted the instrument to something solid, it might get you 10
readings +/- .25" but this is not precision measuring device that is
intended for absolute accuracy.
Also notice that while the readout will show you 0.04 inches, the accuracy
is 0.25 inches. I wouldn't use this to get me any closer then +/- 1 inch.
Bob


www.moondoggiecoffee.com

Finding the keyboard operational
Stubby entered:


The surveyor I used told me the law requires a standard accuracy is
0.1' . A high accuracy measurement gets things to 0.01' .

Stubby, can you get a clarification on that? It seems like getting 1.2
inches accuracy over a 100 foot (1200 inches ) is really tight and .12
inches (about 1/8") really really tight. If we take that to 100 yards (
3600,inches) then the level of accuarcy is 0.00027%. Just doesn't look
right.
Thanks
Bob

--?
--?
Coffee worth staying up for - NY Times
www.moondoggiecoffee.com

What would you be measuring with the laser?
Last time I looked at them (maybe a year ago) they all had really poor
accuracy and were really only good for rough room measurements (as a
real estate agent would use).
If you're building something I'd measure it the old fashioned way.

Vin - Menotomy Vintage Bicycles
http://OldRoads.com

The Other Funk wrote:

Being a handheld device, the error is probably for one reading. If you took
10 readings, while holding it in your hand, You will not get 10 readings +/-
.25"
If you mounted the instrument to something solid, it might get you 10
readings +/- .25" but this is not precision measuring device that is
intended for absolute accuracy.
Also notice that while the readout will show you 0.04 inches, the accuracy
is 0.25 inches. I wouldn't use this to get me any closer then +/- 1 inch.
Bob


www.moondoggiecoffee.com

Accuracy vs. repeatability rears its ugly head...

D

OldRoads wrote:

What would you be measuring with the laser?
Last time I looked at them (maybe a year ago) they all had really poor
accuracy and were really only good for rough room measurements (as a
real estate agent would use).
If you're building something I'd measure it the old fashioned way.

Vin - Menotomy Vintage Bicycles
http://OldRoads.com

I think you're confusing the cheap ultrasonic measuring devices, most of
which have a laser pointer for targeting, with the newer laser measuring
devices which do not use ultrasonic ranging and actually measure with
the laser.

The units mentioned in the Stanley line run from the $100 consumer unit
with 1/4" accuracy and 100' range, to a $450 unit with 1/16" accuracy
and 600' range.

Pete C.

Finding the keyboard operational
entered:

The Other Funk wrote:

Being a handheld device, the error is probably for one reading. If
you took 10 readings, while holding it in your hand, You will not
get 10 readings +/- .25"
If you mounted the instrument to something solid, it might get you 10
readings +/- .25" but this is not precision measuring device that is
intended for absolute accuracy.
Also notice that while the readout will show you 0.04 inches, the
accuracy is 0.25 inches. I wouldn't use this to get me any closer
then +/- 1 inch. Bob


www.moondoggiecoffee.com

Accuracy vs. repeatability rears its ugly head...

D

Add in resolution to the mix and we have got ourselves a mess.

--?
--?
Coffee worth staying up for - NY Times
www.moondoggiecoffee.com

"OldRoads" wrote in news:1153842024.870936.132440
@h48g2000cwc.googlegroups.com:

What would you be measuring with the laser?
Last time I looked at them (maybe a year ago) they all had really poor
accuracy and were really only good for rough room measurements (as a
real estate agent would use).
If you're building something I'd measure it the old fashioned way.

Vin - Menotomy Vintage Bicycles
http://OldRoads.com



If you're building something I'd measure it the old fashioned way.

Yea, closing one eye and giving it a good gander.

On Thu, 27 Jul 2006 22:34:35 -0500, Al Bundy
wrote:

"OldRoads" wrote in news:1153842024.870936.132440
:

What would you be measuring with the laser?
Last time I looked at them (maybe a year ago) they all had really poor
accuracy and were really only good for rough room measurements (as a
real estate agent would use).
If you're building something I'd measure it the old fashioned way.

Vin - Menotomy Vintage Bicycles
http://OldRoads.com



If you're building something I'd measure it the old fashioned way.

Yea, closing one eye and giving it a good gander.

That is how some of the old railroad surveyors did it. Throw a rock
off a cliff and write down the elevation.

--Andy Asberry recommends NewsGuy--