| Chapter 14: Units |

| 14.13. Multiplication of units

Similarly, it is forbidden to multiply 122kg and 10kg, not because it could never make sense (a physicist will occasionally multiply two weights) but because the result is - what? Not a number, and not a weight any more. But we are allowed to tell Inform what the result ought to be, and once we have done so, the multiplication will be allowed:

> A length is a kind of value. 10m specifies a length. An area is a kind of value. 10 sq m specifies an area.

> A length times a length specifies an area.

> The balance platform is in the Weighbridge. "The balance platform is 10m by 8m, giving it an area of [10m multiplied by 8m]."

which will turn up as:

> The balance platform is 10m by 8m, giving it an area of 80 sq m.

And having told Inform that lengths multiply to area, we could also divide an area by a length to get a length: no further instructions would be needed.

Note that we are only allowed to make such a rule about multiplication, and only between units, and the result has to be a unit. So this system cannot be used to make Inform multiply, say, a time by a piece of text, nor to contradict any of the standard "dimensional rules" outlined above.

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| Example Depth Receptacles that calculate internal volume and the amount of room available, and cannot be overfilled.

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