One of the most remarkable facts about a locally compact group "G" is that it carries an essentially unique natural measure, the Haar measure, which allows one to consistently measure the "size" of sufficiently regular subsets of "G". "Sufficiently regular subset" here means a Borel set; that is, an element of the σ-algebra generated by the compact sets. More precisely, a right Haar measure on a locally compact group "G" is a countably additive measure μ defined on the Borel sets of "G" which is "right invariant" in the sense that μ("Ax") = μ("A") for "x" an element of "G" and "A" a Borel subset of "G" and also satisfies some regularity conditions (spelled out in detail in the article on Haar measure). Except for positive scaling factors, a Haar measure on "G" is unique.