Calculating finnish banking reference numbers (Viitenumerot) in ruby

gistfile1.rb

def refnr(source)
	#this takes a ID string with number but declared as string and returns a valid reference number
	
	chk = 0 				#the integrity check number
	weights = [7, 3, 1]		#hash weights, declared by THE GOVERNMENT

	source.split('').reverse.each_with_index { |x, i| chk += (x.to_i)*weights[i%3] }		#does the caluclation
	return "#{source}#{((10-(chk%10))%10)}" #returns the input number with the check number trailing it
end