calculate III record number check digits

iii_calc_checkdigit.rb

# take an string w/ an iii record number without recordtype prefix
# and without check digit and calculate its check digit 
def calc_check_digit(digits)
  digit_seq = digits.split.reverse
  sum = 0
  multiplier = 2
  digit_seq.each { |digit|
    sum += digit.to_i * multiplier
    multiplier += 1
  }
  cdig = sum % 11
  if cdig == 10:
    'x'
  else
    cdig.to_s
  end
end