class StdDev
	declare n
	declare sum
	declare sum2

	def StdDev()
		n = 0
		sum = 0
		sum2 = 0
	end

	def sd(x)
		this.n += 1
		this.sum += x
		this.sum2 += x*x

		return sqrt(sum2/n - sum*sum/n/n)
	end
end

testData = {2,4,4,4,5,5,7,9}
sd = new(StdDev)

for x in testData
	println sd.sd(x)
end