The Gunter’s Scale uses logarithmic and other scales to assist in numerical and trigonometric calculations. Instead of using a sliding scale like the later slide rule to assist in the addition or subtraction of logarithms, the user of a Gunter’s Scale uses dividers to mark sums and differences. The Gunter’s Scale is particularly specialized for nautical use, as some of its scales make direct solution of dead reckoning problems relatively easy. Developed by Edmund Gunter in 1623, Gunter's Scales or Rules continued to be made and used into the 19th century.
This working reproduction of a cross staff shows a scale along the staff and four different length cross pieces, so that different altitudes may be measured precisely. The height of the celestial body to be observed over the horizon determines which scale and arm is used.
The seaman's quadrant was first used at sea around 1460, about twenty years before the astrolabe. It is a quadrant of a circle, made of wood, with a sight up one side, a scale along the arc, and a hanging weight on a string from the apex of the quadrant. The quadrant was used to tell relative distance traveled north or south from a port of departure, something done more easily than measuring an accurate sun height to determine latitude.
The traverse board is used to keep track of changes in a vessel's speed or course over the period of a four-hour watch. At the end of each watch, the courses and speeds are added together, with the help of traverse tables, or by estimation, and marked in the logbook or on a chalkboard. A peg is put into a hole every half hour for the course steered, and another is inserted to reflect the approximate speed sailed. The traverse board, though used some in the sixteenth century, was more common in the seventeenth century.
Mariner's dry card compass, from the schooner Gloucester of Stockton Springs, Capt. George A. Erskine, 1878. This compass may have been made in 1876, the year of the centennial, considering the patriotic artistry on the North point. Like most compasses prior to the 20th century it is laid out in points of 11 1/4 degrees. These 32 points are the result of continually dividing a circle of 360 degrees by 4. Learning the names of the points, called boxing the compass, was an essential skill for a sailor.
Wooden caulking mallet, for driving oakum or cotton into the seam between planks of a wooden vessel, to make the vessel watertight. Used with a caulking iron. Slots cut into the mallet head produce a distinctive ring when the caulking material is seated solidly in the seam.