The astrolabe is an ancient astronomical instrument used to measure the altitude of celestial objects above the horizon, and to determine latitude and longitude. The instrument consists of a circular brass disk, with a graduated scale around the edge, and a movable arm called an alidade. The alidade is pivoted at the center of the disk, and has a pointer that can be used to sight celestial objects. The altitude of an object can be measured by aligning the pointer with the object, and then reading the graduation on the scale that corresponds to the pointer's position.
Cross-staff
The cross-staff is another ancient astronomical instrument used to measure the altitude of celestial objects. The instrument consists of a staff, with a crosspiece perpendicular to the staff. The crosspiece is divided into a number of equal parts, and the staff is marked with a scale of degrees. The altitude of an object can be measured by holding the staff vertically, and then aligning the crosspiece with the object. The number of divisions on the crosspiece that corresponds to the object's position can then be read off the scale on the staff.
Magnetic compass
The magnetic compass is a navigational instrument that uses the Earth's magnetic field to determine direction. The compass consists of a magnetized needle, which is free to rotate on a pivot. The needle aligns itself with the Earth's magnetic field, and the direction of the needle can be used to determine the cardinal directions (north, south, east, and west).
Lead and line
The lead and line is a simple tool used to measure the depth of water. The lead is a weight attached to a cord, and the line is marked with a scale of fathoms or feet. The depth of water can be measured by lowering the lead into the water until it touches the bottom, and then reading the graduation on the line that corresponds to the water's surface.
Sand glass
The sand glass is a simple device used to measure time. The sand glass consists of two glass bulbs connected by a narrow neck. The top bulb is filled with sand, and the bottom bulb is empty. When the sand glass is turned over, the sand flows from the top bulb to the bottom bulb, and the amount of time that it takes for the sand to flow through can be used to measure time.