The Riemann surface for the complex version of this is a helix-like plane spiraling around the z axis; in hyperbolic geometry, this function is in the distance formula for the geodesic between two points. First defined to contain a "mantissa" by John Napier, this function is equal to the antiderivative of one over x. Increments on the slide rule increase according to this 
The Riemann surface for the complex version of this is a helix-like plane spiraling around the z axis; in hyperbolic geometry, this function is in the distance formula for the geodesic between two points. First defined to contain a "mantissa" by John Napier, this function is equal to the antiderivative of one over x. Increments on the slide rule increase according to this function using its product-to-sums property, and dividing one by another allows for a change of base. For 10 points, identify this function which, when found in base e form, is known as "natural," the inverse of the exponential function.
The Riemann surface for the complex version of this is a helix-like plane spiraling around the z axis; in hyperbolic geometry, this function is in the distance formula for the geodesic between two points.
natural logarithm [prompt "ln" or "lon"]