a unit of information content used in information and communications theory. The hartley is similar to the shannon. If the probability of receiving a particular message is , then the information content of the message is -log10 hartleys. For example, if a message is a string of 5 letters or numerals, with all combinations being equally likely, then a particular message has probability 1/365 and the information content of a message is 5(log10 36) = 7.7815 hartleys. One hartley equals log2 10 = 3.321 928 shannons or loge 10 = 2.302 585 nats.