What is Holmesian deduction?

Holmes stories often begin with a bravura display of his talent for “deduction”. It is of some interest to logicians and those interested in logic to try to analyze just what Holmes is doing when he performs his deduction. Holmesian deduction appears to consist primarily of drawing inferences based on either straightforward practical principles – which are the result of careful inductive study, such as Holmes’s study of different kinds of cigar ashes or inference to the best explanation.