The Collaborative International Dictionary of English v.0.48:
Arithmetical \Ar`ith*met"ic*al\, a. Of or pertaining to arithmetic; according to the rules or method of arithmetic. [1913 Webster] Arithmetical complement of a logarithm. See Logarithm. Arithmetical mean. See Mean. Arithmetical progression. See Progression. Arithmetical proportion. See Proportion. [1913 Webster]