circular slide rule

[Will Ware]

"""This generates a Postscript file, which when printed on
an 8.5x11 sheet of paper, gives you a circular slide rule.
Without the transparent slider, it's probably a lot less useful
than a log table, but there may be some nostalgic fun in here
for somebody."""

import sys, math

center = (72 * 4.25, 72 * 5.5)

def p2r(r, theta):
    t = math.pi * theta / 180.
    return (r * math.cos(t) + center[0],
            r * math.sin(t) + center[1])

print '%!PS'
print '/Times-Roman findfont 10 scalefont setfont'

def axis(theta):
    x1, y1 = p2r(0, theta)
    x2, y2 = p2r(72 * 4, theta)
    print '%g %g moveto %g %g lineto stroke' % (x1, y1, x2, y2)

def span(xlim, dx, n):
    global x
    i = 0
    while x + 1.e-8 < xlim:
        nextx = x + dx
        if i == 0:
            label = '%.3g' % x
            gap = 4
        else:
            label = ''
            gap = 2
        L1 = math.log10(x)
        L2 = math.log10(nextx)
        r1 = (72 * 3.5) - L1 * (72 * 1)
        r2 = (72 * 3.5) - L2 * (72 * 1)
        th1 = 720 * L1
        th2 = 720 * L2

        x1, y1 = p2r(r1, th1)
        x2, y2 = p2r(r2, th2)
        x3, y3 = p2r(r1 + gap, th1)
        x4, y4 = p2r(r1 - gap, th1)
        print '%g %g moveto gsave %g rotate' % (x3, y3, th1)
        print '( %s) show grestore' % (label)
        print '%g %g moveto %g %g lineto stroke' % (x1, y1, x2, y2)
        print '%g %g moveto %g %g lineto stroke' % (x3, y3, x4, y4)

        x = nextx
        i = (i + 1) % n

def magnitude():
    x0 = x
    span(1.5 * x0, .005 * x0, 4)
    span(2 * x0, .01 * x0, 5)
    span(4 * x0, .01 * x0, 10)
    span(7 * x0, .02 * x0, 5)
    span(10. * x0, .05 * x0, 5)

print '.7 setgray'
for i in range(36):
    axis(i * 10)

print '0 setgray'
x = 1.
magnitude()
magnitude()

span(x + 0.00001, .001, 1)

print 'showpage'
-- 
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Resistance is futile. Capacitance is efficacious.
Will Ware	email:    wware @ world.std.com