Abstract: The claimed calculus teaching and demonstration device has an internal volume in the shape of two perpendicular axes and a mathematical function that can be filled with a measured amount of liquid and thus used to illustrate the calculus concept of area under the curve.

Abstract: Sextant telescope with a zoom feature is a device in which one of two available magnification settings is selected by repositioning an internal lens between two mutually conjugate locations. An optional reticle of a specialized pattern helps the proper alignment of the observed horizon and celestial bodies in the field of view of the telescope for easier and more accurate measurements; the placement of the reticle in the first focal plane ensures proper scaling of its apparent size with telescope magnification.

Abstract: The T-plotter is a T-shaped transparent plotting utensil consisting of two mutually perpendicular arms and equipped with a rotatable compass rose mounted on a shuttle sliding along its arm of symmetry. This device allows a simplified plotting of celestial lines of position according to the intercept method of Marcq St. Hilaire. The compass rose is used to dial in the required azimuth. The intercept distance is marked by sliding the shuttle to the appropriate distance from the top of the main body based on the latitude scale of the employed nautical chart.