stdDev :: Double -> Double -> Double
stdDev x y = sqrt ((x - avg x y) ^ 2 + (y - avg x y) ^ 2) / 2
stdDev :: Double -> Double -> Double
stdDev x y = sqrt ((x - avg x y) ^ 2 + (y - avg x y) ^ 2) / 2
stdDev x y = sqrt ((x - avg x y) ^ 2 + (y - avg x y) ^ 2) / 2