# Feel dumb asking this but... (Math question)

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Im interested in a glass bead screen for my CRT projector.

Im good at math, but awful at geomotry...

What is the equation to figure out 30 degrees using only tape measure measurements?

I dont have any other way of doing it with the tools I have

John
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A triangle with sides of 1, 0.5 and 0.866. The narrowest angle with be 30 degrees.

-Dylan
John,

In the real world heads with eyes don't sit in exactly 30 degree positions.

You could take a 90 degree angle fairly easily then just use 1/3 of that. This will give you a very close approximation of where this point would be.

Don't get too hung up with the exactness of the math/geometry.
Where do you find these heads with eyes?

Mark
Aztechjohn

The easiest way to maintain a 30-degree viewing angle is to affix a string to each side of your screen located at your viewing height. Now cut each string with a measured length equal to the width of your screen divided by 0.5176. Now stand back from the screen and gently locate the point of intersection for both strings so that they are each taut and touching. At this point you will have subtended a 30-degree viewing angle to your screen and that point will be located dead centre to the screen (you have just created an isosceles triangle).

Peter
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