A magnifying glass is used mainly to aid the instrumentman in reading graduations that are provided with verniers, such as the horizontal and vertical circle of a transit. Although these graduations can be read with the naked eye, the use of a magnifying glass makes the reading easier and decreases the chance of reading the wrong coincidence.

Two types of magnifying glasses that you will generally find in the transit box are shown in figure 11-54. They are usually called pocket

magnifying glasses. To avoid unknowingly dropping a magnifying glass in the field, you should attach it to a loop of string. The instrumentman puts his head through the loop, retaining the string around the neck, and carrying the magnifying glass in a pocket. At the end of each days work, it is a good practice always to return the magnifying glass to its proper place in the instrument case.

Surveying instruments are built in such a way that minor adjustments can be performed in the field without much loss of time while the work is in progress. The adjustments are made by loosening or tightening the capstan screws that are turned by the use of adjusting pins. These pins are also included in the instrument box. They come in various sizes that depend upon the type of instrument and the hole sizes of its capstan screws. Use the pin that fits the hole in the capstan head. If the pin is too small, the head of the screw will be ruined.

Replacements for these pins are generally given free of charge by surveying instrument dealers. Like the magnifying glass, adjusting pins should be carried in the pocket and not left in the instrument box while a survey is in progress. This will save a lot of valuable time when the pins are needed. Do not use wires, nails, screwdrivers, and the like, as substitutes for adjusting pins.