The "tertiant" is a simple astrolabe similar to the quadrant or sextant. It is useful for measuring unreachable altitudes, discovering local latitude, and finding the average of inclines.
This is the only Tertiant known to exist. The quadrant and sextant measure angles less the 90 degress. This astrolabe measures a full 120 degrees allowing the intrepid airship explorer to aim not only above, but also below.
Instructions: Look through the eyepiece, and line up your target with the sites (ie. north star for latitude, the top of a building or tree for altitude). When you do this, the dial will adjust itself by gravity to point out a degree on the guage. Zero is indicated by the vertical bar. Each second degree is marked by a small bar at the bottom of the guage, and these are grouped in ten degrees.
note: Before I release this for sale, I will be adding numbers on the guage, a ring at the top for hanging, and a ring on the end of the dial to hang a weight for more accurate readings.