[[P3045R10]](https://wg21.link/p3045r10) models quantities with two abstractions, a delta and a point, both spelled with the `quantity` class template: `quantity<R>` is a delta and `quantity<point<R, PO>>` a point. Neither fits the most common value in a physics equation, an amount measured from a true zero, such as a mass of 5 kg or a thermodynamic temperature of 300 K. A delta has no zero anchor, and two points can’t be added, and a point can’t be multiplied or divided.