[Woodcarver] Geometry question for the group

[Byron Kinnaman]

Ahhhh, Pardon me, but I believe the original question was to make a 13 point star using only a straight edge (not a ruler with measurements) and a compass or divider. Again there are no numbered increments. 

Good luck,
Byron



Opps .. It would have been nice if I had included the formula in the
earlier e-mail ... My apologizes.

A circle's circumference is equal to the diameter divided by pi (3.14).
C=pi/d  My computer doesn't have a pi key.
Radius is one half of the diameter.  d=1/2r

The circumference of a circle is 13 inches. What is the diameter? 
   
Solution:  
  13 inches = 3.14 · diameter
  13 inches ÷ 3.14 =  diameter  = 4.140 inches diameter = radius of 2.07
inches

For multiples of 13 use 26 or 39 and then use 2" spacing for 26"
circumference or 3" spacing for 36".
  26 inches = 3.14 / diameter = 8.280 inches diameter = radius of 4.140
inches
  39 inches = 3.14 / diameter = 12.420 inches diameter = radius of 6.21
inches 

I note this only because the I believe that those of 800 years ago had a
touch more than just straight edges and compasses.  I would expect that
they had defined measuring units (rulers) and they had some excellent
higher math skills.

Susan