Variability and Complexity
We define as "variability" the number of the potential discrete states of a system. Variability depends on the scale in which the system is observed, as slight alterations which are observable—consequently make possible the identification of discrete states—in the small scale, are not observable in the large scale. As a consequence, variability tends to decrease with the scale of observation. The "complexity" of the system, defined as the logarithm of the value of variability, determines the quantity of the information contained in the system. Due to this definition, complexity also depends on the scale of observation.
Bar‑Yam Y., 1997, Dynamics of Complex Systems. Addison Wesley, Reading, Massachusetts, pp. 12-14