English: A page from Mirifici logarithmorum canonis descriptio by John Napier. The left-most column gives minutes to be added to the angle for this page, 34 degrees. The far right column is the co-angle (90° - x). This page covers 30 to 60 minutes; a facing page covers 0 to 30 minutes. Adjacent to each outer column is the sine of that angle, followed towards the middle by the absolute value of natural log of the sine. One can get cosines easily by reading across the page from the co-angle. In the middle column is the difference between the two logs, which is the natural log of the tangent function (cotangent if you reverse sign).^[1]