anchor.diff:          let l:float = degToRad lon
           let t1 = degToRad centerlat // latitude center of projection
           let l0 = degToRad centerlon // longitude center of projection
  -        let c = Math.Acos ((sin t1) * (sin t) + (cos t1) * (cos t) * (cos (l-l0)))
  +        let c = acos ((sin t1) * (sin t) + (cos t1) * (cos t) * (cos (l-l0)))
           let k = c / (sin c)
           let x = k * (cos t) * (sin (l-l0))
           let y = k * (cos t1) * (sin t) - (sin t1) * (cos t) * (cos (l-l0))
  
positive.code:         let costcosll0 = (cos t) * (cos (l-l0))
          let sint = sin t
          let sint1 = sin t1
          let c = Math.Acos ((sint1) * (sint) + (cost1) * costcosll0)
          let k = c / (sin c)
          let x = k * (cos t) * (sin (l-l0))
          let y = k * (cost1) * (sint) - (sint1) * costcosll0
  
negative.code:         let l = degToRad lon
          let t1 = degToRad centerlat // latitude center of projection
          let l0 = degToRad centerlon // longitude center of projection
          let c = acos ((sin t1) * (sin t) + (cos t1) * (cos t) * (cos (l-l0)))
          let k = c / (sin c)
          let x:float<x> = k * (cos t) * (sin (l-l0)) 
                           |> LanguagePrimitives.FloatWithMeasure
  