Constant Function Years 1 - 8

Children are always fascinated by the Constant Function of a calculator which constantly repeats the last operation it was asked to do if the [=] button is constantly pressed.

• We can make use of this interest to encourage a little thinking.
• The way the constant function is accessed could be different to the examples given here.
• If unsure, check the instructions - or ask the children!

Procedure

Press [+] then a number. eg:

[+] then [4] followed by [=] gives 4 on the screen.

The reason is that when you turn on the calculator, there is a zero on the screen. When you press [+] [4] the calculator needs to add the 4 to something. It has been programmed to add it to the screen number. Pressing [=] has been programmed to mean [repeat the previous operation].

Now press [=] again. The calculator will repeat the previous operation ... [+] [4] ... to give an answer of 8. With each on-going press of [=] another [+] [4] will occur until the operation is changed, or cleared.

• Can you predict the next number?
  • Guess then check.
• How many times will you press [=] to reach 40?
  • Guess then check.

Discuss and record the patterns noticed.

Variations

1. Subtraction using the constant function. eg:

[1] [0] [0] [0] [-] [1] [0] [=]

990

[=]

980

[=]

970 ...

2. Doubling, eg:

[2] [x] [3] [=]

6

[=]

12 ...

3. Halving, eg:

[1] [0] [0] [0] [÷] [2] [=]

500 ...

4. Close Your Eyes Counting

• An example is to start with zero on the screen and teach the calculator to count forward by 7 (say) by pressing [+] [7].
• Now, close your eyes and press [=] until you think the screen will show 84 (say).
• Open your eyes. Were you correct?
• Try counting backwards.