Why can I not type a number into the whole?

Because then it could disagree with the parts. The whole is the sum of the parts and the tool keeps it that way, so whatever is on the board is always true. The Whole buttons are there and they work by changing the last part, which is the only reading that stays consistent.

How do I set a missing number question?

Set all the numbers first, then tap the circle you want to be the question. It turns grey with a question mark. Cover the whole for an addition, or a part for a subtraction.

Can I use it for bonds to 100?

Yes. Set Steps of to 10 and the buttons move in tens, so bonds to 100 take a couple of taps each. Parts go up to 999.

Part-Whole Model

Number · Reception–Year 4

Number bonds as a whole and its parts. Cover a circle to ask the question.

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About the part-whole

The whole on top, its parts below, joined by lines. It is the picture number bonds are taught with, and the one children meet again for missing numbers, for the inverse relationship between adding and subtracting, and for partitioning.

The whole is always the sum of the parts, and there is no way to make it anything else. That is deliberate. A model where you type a number into every circle will happily show 6 and 4 under a whole of 12, and a diagram that can lie about the one relationship it exists to show is worse than no diagram. So you set the parts and the whole follows.

The question is posed by covering rather than by leaving a circle blank. Set 6 and 4, tap the 4, and the board asks the class: the whole is 10 and one part is 6, so what is the other part? Tap it again to reveal. Cover the whole instead and it is an addition; cover a part and it is a subtraction, from exactly the same picture.

Three parts is there for partitioning. With steps of 100, 10 and 1 you can build 456 as 400 and 50 and 6 in six taps, which is the same diagram doing a Year 3 job.

How to use it on your whiteboard

1Use the plus and minus buttons to set each part. The whole adds itself up.
2Tap any circle to cover it. Tap it again, or Show all, to reveal.
3Parts switches between two circles and three.
4Steps of sets the buttons to move in 1s, 10s or 100s.
5Tap Fullscreen so the model fills the board.

Questions

Why can I not type a number into the whole?: Because then it could disagree with the parts. The whole is the sum of the parts and the tool keeps it that way, so whatever is on the board is always true. The Whole buttons are there and they work by changing the last part, which is the only reading that stays consistent.
How do I set a missing number question?: Set all the numbers first, then tap the circle you want to be the question. It turns grey with a question mark. Cover the whole for an addition, or a part for a subtraction.
Can I use it for bonds to 100?: Yes. Set Steps of to 10 and the buttons move in tens, so bonds to 100 take a couple of taps each. Parts go up to 999.