The Barrett Scale
The Barrett Scale was introduced in The Courier magazine in the 1990's to provide a reliable system for identifying sizes in their figure reviews.
"The Courier uses the Tobey Barrett Measurements System (BM) to simplify the comparison of figure sizes one to another. Briefly the number is the height in Millimeters from the bottom of the figure's foot (top of the base) to it's eye. The letter refers to the "heft" of the figure: L = Light; M = Medium; and H = Heavy. H will fit well with other H and somewhat with M but not at all with L even in the same scale. thus a 27 M is a larger 25mm figure of Medium Heft."
BM figure sizes for each manufacturer may vary from range to range, and sometimes even among different figure codes of a single range.