As a rodman, you must concentrate on keeping your rod perfectly plumb. Readings on a rod that is out of plumb are inaccurate. Similarly, as a levelman, you must constantly bear in mind that the line of sight through the telescope must be perfectly level in every direction or every reading you make with the instrument will be inaccurate. After you initially place the instrument, level it carefully as follows: Train the telescope in line with a pair of level screws and manipulate the level screws by turning them in opposite directions, as shown in figure 14-7, until the bubble in the level vial is in the exact center. It is helpful to know that the bubble in the level vial will move in the direction that your left thumb moves. To put this another way: When you turn the left-hand screw clockwise, the bubble moves to your left; when you turn the left-hand screw counterclockwise, it moves to your right. When the bubble is centered with the telescope over one pair of screws, train the telescope over the other pair and repeat the process. As a check, swing the telescope over each pair of screws in all four possible positions to make sure the bubble is centered in each position.

The instrumentman makes a direct rod reading as viewed directly on the graduation of the rod (self-reading) that is in line with the horizontal

Figure 14-8.-Showing a direct reading of 5.76 ft on a Philadelphia rod.

cross hair. A rod other than an architects rod is usually graduated in feet subdivided to the nearest 0.01 ft; therefore, direct readings are possible only to the nearest 0.01 ft.

Figure 14-8 shows a direct reading of 5.76 ft on a Philadelphia rod. You can see that each black graduation and each white, interval represents 0.01 ft.

You can see also that the black figure 7 is the only numeral of the reading 5.76 ft that appears in the view. The red numeral 5 would not be visible through the telescope unless the sight distance was quite far away. For this reason, you would signal the rodman to "raise for red," as described in the previous chapter.

To make sure you relate the reading for tenths and hundredths to the correct whole-foot red numeral, it is best to make a direct reading as follows: When the horizontal cross hair and the rod are brought into clear focus, first determine the number of hundredths. Then, read the next lower black figure for the tenths. Finally, signal for a "raise for red," and note the number of whole feet.