What is Absolute and relative uncertainty?

A measurement of a quantity $x$ is stated as

where $x_{\text{m}}$ is the measured value and the absolute uncertainty $\Delta x > 0$, in the same unit, bounds the plausible error: the true value is claimed to lie between $x_{\text{m}} - \Delta x$ and $x_{\text{m}} + \Delta x$. The relative uncertainty is the ratio $\Delta x / x_{\text{m}}$, usually quoted in percent; it is what the word “precise” measures.