The angles are taken with a sextant from the back of a boat, a less than stable platform. The degree of accuracy is dependent on the less than perfect human eyesight, sea, fog , weather conditions and again the placement of the beach markers. When all the information is finally compiled, the next step is to plot the location on a base map. This is done with the use of a three arm protractor called a tritractor. To make the tritractor usable for the majority of site areas, the arms of the tritractor must be extended by means of glue, tape or even staples.
Most sites are too large to use the tritractor as it is meant to be used, hence the extensions.
These extensions render the tritractor useless to any degree of accuracy. Another way of plotting, other than the tritractor, is to use a mathematical formula called a three bearing fix . This is done using the distance between the beach markers and the angles from a boat to the beach markers. This formula gives only the tangent of the angle. The tangent must then be converted to one angle.