Boltzmann's equation is presumed to provide a link between thermodynamic entropy "S" and information entropy "H = −Σi pi ln pi" = ln(W)" where pi=1/W" are the equal probabilities of a given microstate. This interpretation has been criticized also. While some say that the equation is merely a unit conversion equation between thermodynamic and information entropy, this is not completely correct. A unit conversion equation will, e.g., change inches to centimeters, and yield two measurements in different units of the same physical quantity (length). Since thermodynamic and information entropy are dimensionally unequal (energy/unit temperature vs. units of information), Boltzmann's equation is more akin to "x = c t" where "x" is the distance travelled by a light beam in time "t", "c" being the speed of light. While we cannot say that length "x" and time "t" represent the same physical quantity, we can say that, in the case of a light beam, since "c" is a universal constant, they will provide perfectly accurate measures of each other. (For example, the light-year is used as a measure of distance). Likewise, in the case of Boltzmann's equation, while we cannot say that thermodynamic entropy "S" and information entropy "H" represent the same physical quantity, we can say that, in the case of a thermodynamic system, since "kB" is a universal constant, they will provide perfectly accurate measures of each other.