/**
   The fundamental equation of a slide rule on the C and D scales is:

   distance1 = scale * log[n1/n0]

   Where distance is the actual distance to mark a point with units of length
   on a physical slide rule given an arbitrary dimensionless number n1 and a
   "start point" dimensionless number n0 (which may be 1, or 1000 on large
   circular slide rules.)

   Scale is a scale with units of length, e.g. "scale = 10 inches" makes a
   "10 inch slide rule" where a multiplicative scale of 10 from the start point
   is 10 inches from the start point.  This is interesting and gives an actual
   physical scale to slide rules based on logarithms to base 10.

   In log base 10 (log function):
      distance1 === scale log[n1/n0]
      n1 === n0 10^(distance1/scale)
      scale = distance1 / log[n1/n0]

   or, in natural log (ln function):
      distance1 === scale ln[n1/n0] / ln[10]
      n1 === n0 e^((distance1/scale) ln[10])
      scale === distance1 ln[10] / ln[n1/n0]


   WARNING:  The equations below are not quite right.

   For a circular slide rule, the radius probably should be written as an
   Archimedan spiral:
   See:
   https://www.comsol.com/blogs/how-to-build-a-parameterized-archimedean-spiral-geometry/
   
   radius = a + b theta

   or

   b = (radius2 - a) / (2 pi + theta1)
   a === -2 b pi + radius2 + -1 b theta1
   radius2 === a + 2 b pi + b theta1
   theta1 === -1 a b^-1 + -2 pi + b^-1 radius2

   or in [x, y] coordinates:

   x = (a + b theta) cos[theta]
   y = (a + b theta) sin[theta]
*/

p = new polyline
a = 1 inch
theta1 = 90 deg
radius2 = 2 cm
b = abs[(radius2 - a) / (2 pi + theta1)]
println["b is $b"]
for theta = 0 to 8 circle step 2 degree
{
   x = (a + b theta) cos[theta]
   y = (a + b theta) sin[theta]
   p.addPoint[x,y]
}

p.show[]