Where does the carried digit go?

Under the line, in the column it is carried into. That is the way it is written in England and in every scheme of work here, and it keeps the carrying out of the way of the digits being added.

Why does it not just show the answer?

Because the answer is not the thing being taught. A class that can see the finished sum has been shown what column addition looks like, not how it goes, and the reveal is the only part a board can do better than a book.

Can it do numbers with more than four digits?

Not yet. Four is the Year 4 objective and the point at which the method is being taught rather than practised, and a longer sum uses exactly the same steps. If you need five and six digit numbers on the board, say so and they can go in.

Why does it swap the numbers when I choose subtraction?

Because the top number has to be the bigger one and the alternative is telling you off. If you change a digit afterwards and make the top number smaller, the board says so and waits.

Column Addition and Subtraction

Calculation · Year 3–Year 6

Work a column sum out one column at a time, carrying as you go.

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About the column method

Two numbers, one under the other, and nothing worked out until you ask for it. Press Next and one column is done: the digit goes under the line, the carry goes where it belongs, and the line at the top says what just happened in the words a teacher would use.

The order is the whole lesson. A finished sum on a board teaches nothing, because what a class loses the thread of is the choreography: which digit you write down, which one you carry, and what you do when the column you need to take from is empty. That is the one thing a worksheet cannot show and a board can.

Set the numbers on the board itself. Each digit has a chevron above and below it: press the top half to put it up, the bottom half to put it down. New gives you a fresh sum that actually carries, because a random sum with no carrying in it is the one kind not worth doing.

Subtraction shows the exchange the way it is written: the digit crossed out and what it now counts as written above it. Take one away from three hundred and you can watch it go next door twice, which is the case every class gets stuck on.

The carried digit goes under the line, in the column it is carried into, which is how it is written in England. Guides rules the columns faintly, like the squares in an exercise book.

How to use it on your whiteboard

1Press the top half of a digit to put it up, the bottom half to put it down.
2Choose + or − for the operation.
3Next works out the next column, Back takes it off again.
4None starts the working again. All works the whole sum out.
5New gives you a fresh sum with some carrying in it.
6Tap Fullscreen to fill the board.

Questions

Where does the carried digit go?: Under the line, in the column it is carried into. That is the way it is written in England and in every scheme of work here, and it keeps the carrying out of the way of the digits being added.
Why does it not just show the answer?: Because the answer is not the thing being taught. A class that can see the finished sum has been shown what column addition looks like, not how it goes, and the reveal is the only part a board can do better than a book.
Can it do numbers with more than four digits?: Not yet. Four is the Year 4 objective and the point at which the method is being taught rather than practised, and a longer sum uses exactly the same steps. If you need five and six digit numbers on the board, say so and they can go in.
Why does it swap the numbers when I choose subtraction?: Because the top number has to be the bigger one and the alternative is telling you off. If you change a digit afterwards and make the top number smaller, the board says so and waits.