A semi-logarithmic reference mark is a reference mark in which one of the axes, for example that of the X-coordinates (X), is graduated according to a linear scale, like the graduations of one linear meter, whereas the other axis, here that of the ordinates (there), is graduated according to a logarithmic scale.

The semi-logarithmic reference mark makes it possible to represent exponential phenomena or, more generally, measurements which can take values close to 1 or close to $10^5$

Example: Chart of the terms of the continuation $(2^n)\; \_\; \{n=1\dots \; 8\}$ in a semi-logarithmic reference mark.

This type of reference mark also makes it possible to evaluate growth rates of a variable evolving/moving with time. Whatever the level of the variable, of identical growth rates will be represented by segments having the same slope. One can thus compare growth rates by disregarding scale effect.

See too