Knowing that there were many errors in the calculation of mathematical tables, Babbage wanted to find a way to calculate them mechanically, removing errors made by humans. Three different factors seem to have influenced him: a dislike of untidiness; his experience working on logarithmic tables and differential calculus; and work on calculating machines already done by Wilhelm Schickard, Blaise Pascal, and Gottfried Leibniz. He first talked about the principles of a calculating engine in a letter to Sir Humphrey Davy in 1822.