A “concrete scale” is a technique that can be used to visually relate, re-express, and compare measures of extreme magnitudes or unfamiliar units.
Concrete scales use familiar and culturally appropriate visual metaphors to depict simple relationships of complex measurements, making it easer for a viewer to comprehend the measure.
Examples of this are: conversion/comparison, containment/nesting, unitization (defining an object as a new unit of measure), and analogy.
For more about concrete scales, see Using Concrete Scales: A Practical Framework for Effective Visual Depiction of Complex Measures.