There is some variation in the constant function in different
  calculators so you may need to experiment a little to find out
  how to work it. For example, with some older calculators the key
  sequence is 1 + + = = <br />
  Children as young as 5 years will happily use the constant
  function as long as they are sure of the correct sequence of
  keys, so practice the steps and count aloud with them before
  posing the problem. <br />
  You may find it useful to incorporate a hundred chart and have
  the children place a counter on each number to match the numbers
  appearing on the calculator. This can lead on to further
  exploration of the visual patterns produced by the counters on
  the chart. Older children can link this 'skip counting' to
  multiples, factors and multiplication tables. <br />
  The task can be varied by changing the target number to another
  number with several factors (e.g. 48) or to a prime number (e.g.
  31). More advanced children can be challenged by a much larger
  number (e.g. 744 or 2 308) which will require the invention of
  strategies for guessing or figuring out possible factors. They
  will also need to find a way (other than counting) to test their
  'guesses' - such as using division. <br />
  The constant function can also be used for counting on from a
  chosen starting number. Unless another number is keyed in, the
  counting starts from zero. For example: to start counting by twos
  starting from 5, key in 5 + 2 = = and produce the sequence<br />
  <br />
  5 7 9 11 13. <br />
  <br />
  Many more mathematical discoveries can be made by using the
  constant function with other operations.<br />