A unit of information used in information theory, equal to the logarithm base 10 of the number of possible equally likely messages. Also a surname of English origin.
Named after Ralph Hartley (1888-1970), an American electronics researcher who made contributions to information theory. The surname derives from Old English 'heorot' (hart/stag) + 'leah' (wood, clearing), meaning 'stag's meadow'.
The Hartley unit predates the more famous 'bit' by decades and uses base-10 logarithms instead of base-2, making it more intuitive for decimal calculations. One Hartley equals about 3.32 bits, bridging the gap between human decimal thinking and computer binary processing.
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