# From what part of a circle, or other constant or formula, does the formula 1718.87/radius, derive?

1718.87 divided by the radius of a circle gives you the deflections per minute per foot of arc, for laying out points on a curve with a transit or theodolite. I can't remember how the 1718.87 number is derived, but it has to do with other curve information, such as 5729.577 divided by the diameter of a circle gives you the radius of the circle, etc.

I'm not familiar with your formula but your number 1718.87 is just the number of arc minutes in a circle (360*60) divided by 4π. The deflection 'd' of a curve of radius 'r' over angle 'a' is

The arc length 'L' for a circle of radius 'r' is related to the angle in radians 't' by:

t = L/r

The angle in arc minutes 'a' is related to the angle in radians by:

a = 180*60*t/π = 3437.74 t

So the angle in arc minutes defined by the arc length 'L' is:

a = 3437.74 L/r

This is exactly twice the number you mentioned (1718.87). I'm not sure what you mean by "deflection" I'm not a surveyor so I can't figure where the factor of 2 comes from.

On your second question, there must be some mistake since diameter divided by 2 is radius.

More Questions and Answers:

More Questions and Answers:

how do we construct stone arch bridges?
tell me which material is best in semiconductor si or Ge?
what is potable pipe?
which is more elastic steel wire or rubber chord? why?
What does 'EDS in still air' mean?
derive the null condition for wheatstone bridge?
Seems to be a lot of static electricity these days.?
Where is the best engineering school?
A certain light bulb with a resistence of 95 ohms is labeled 150 W. Was this bulb designed for use in a 120 V?

**Answer:**I'm not familiar with your formula but your number 1718.87 is just the number of arc minutes in a circle (360*60) divided by 4π. The deflection 'd' of a curve of radius 'r' over angle 'a' is

The arc length 'L' for a circle of radius 'r' is related to the angle in radians 't' by:

t = L/r

The angle in arc minutes 'a' is related to the angle in radians by:

a = 180*60*t/π = 3437.74 t

So the angle in arc minutes defined by the arc length 'L' is:

a = 3437.74 L/r

This is exactly twice the number you mentioned (1718.87). I'm not sure what you mean by "deflection" I'm not a surveyor so I can't figure where the factor of 2 comes from.

On your second question, there must be some mistake since diameter divided by 2 is radius.

The answers post by the user, for information only, FunQA.com does not guarantee the right.

More Questions and Answers:

More Questions and Answers: