Would a Laser "tape" measure…?

by admin on April 1, 2010

Would a Laser "tape" measure purchased from, say, Home Depot measure near to the exact distance of path lengths if it aimed through a thin film? How accurate are these devices?

This just a curious question, so please no interferometry type explanations.

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{ 5 comments… read them below or add one }

jpricefam1 April 1, 2010 at 4:32 am

First of all, the "laser" tape measures that they sell at Home Depot are not laser based at all. They use ultrasonic reflectometry. The laser is a simple pointer. The measurement is made by an ultrasonic pulse that reflects off of a flat surface and the distance is calculated by the time it takes from the start of the pulse to the time of return of the reflected pulse. This time is divided by the speed of sound in air (1130 f/s @ 70 degrees F) to give the distance. The resolution of these intruments is +/- ~1".

whitetrashwithmoney April 1, 2010 at 4:32 am

As long as the filim is really thin. A good on is good to ten-thousandth of an inch at 100 ft

Justin c April 1, 2010 at 4:32 am

i have on it isnt persice it won’t measure anything less that two feet and rounds to the mearest inch
ps i got mine from home depot

lone April 1, 2010 at 4:32 am

the laser probley could not mearser thro something like film even if it did go thro it so you will probley have to find some other way to do that but they are accurate when used to the task intended hope that helps

farrell_stu April 1, 2010 at 4:32 am


If there is some reflection due to the thin film then it will measure the distance to the thin film. As well it should measure the distance to the further object.

I belive that the prosses works by measureing the time that it take the beam to go from one place to another.

Thus It would measure a reflection from the thin film and to the object beyond it.

I belive that It would either give you an error message or would average the two distances( sort of) . If the film is 33% reflective it would measure a pulse of 33 units from the film, and then 33 from the wall behind it (remember that there will be relfection again when the beam travels back through the film. So you would measure a distance of exactly half way between.

If it is more refective it would measure closer to the film, If it is less relfective then It would measure a distance that is closer to the wall.

As I said either that or give an error. I would be interested if some one would try it out and give their result.

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