Determining the phase of the moon for any given date
Notes: "The Moonstick is an unusual slide rule in that it has no logarithmic scales and it performs just one task: determining the phase of the moon on any given date within a 16,000-year range. The rule consists of six rods, numbered 0 to 5, each with an equilateral triangle cross section. Two rings are permanently attached to the 0 rod, and the other five rods slide in to the rings to form a bundle with a hexagonal cross section. In use it is simpler than it appears. The slides are moved sequentially to input the year, the month, the offset from UTC (Greenwich Mean Time), and then the phase of the moon can be read next to the day of the month. Depending on the date you're interested in, you may have to remove a slide, rotate it, and put it back in so that the color of the arrow matches the color of the year's digit. "
