When $2$ number's ratio can not be expressed as a rational number then we call these number incommensurable.
But I also read that incommensurable also has the meaning of being able to measure two numbers by the same standard.
For example we have $$\frac{3}{4}= 0.75 \implies 3 = 0.75 \cdot 4 \\\And\\
4=\frac{16}{3}\cdot 0.75 $$
So they are both multiple of $0.75$
But what is the principle that this is based on?