procedure main(av)
    if match("-fpp=", av[1]) then
	onePixelFt := numeric(pop(av)[6:0])
    else
	onePixelFt := 10.33 / 54
	# 45' / 78 pixels = 0.26 feet per pixel
        # the default on NMSU's sh1.gif
#	onePixelFt := 45 / 78.0

    if match("-origin=", av[1]) then {
	origin := pop(av)[9:0]
	origin ? {
	    originx := integer(tab(many(&digits)))
	    =","
	    originy := integer(tab(many(&digits)))
	}
    }
    else {
	originx := 188
	originy := 60
    }


    &window := open("Frank Harary Normal Calculator, v2","g",
		    "image=" || (av[1] | "2.gif"))|
	stop("usage: fhn [-fpp=n] [-origin=x,y] floor_plan_file.gif")
    Fg("red")
    DrawSegment(44,19, 46, 21, 46, 19, 44, 21)

    sx1 := 294
    sy1 := 252

    sx2 := 372
    sy2 := 252

#    WAttrib("label=Scale: one pixel = " || onePixelFt || " feet")
#    delay(4000)
    onePixelMt := onePixelFt / 3.281
    WAttrib("label=Scale: one pixel = " || onePixelMt || " meters. Click any pixel for its FHN.")

    while (e := Event()) ~=== "q" do {
	if e === (&ldrag | &rdrag | &mdrag) then next
	x := (&x - originx)
	y := (&y - originy)
	if x === lastx & y === lasty then next
	# write("FHN(",&x,",",&y,") [base ",x,",",y,"]: ", x * onePixelFt, " , ", y * onePixelFt, " in feet")
	write("FHN(",&x,",",&y,") [base ",x,",",y,"]: ",
	      x * onePixelMt, " , ", y * onePixelMt, " in FHN meters")
	lastx := x
	lasty := y
    }
end