introduction
the cities where they have been manufactured: they are called Philadelphia, Chicago, San Francisco, and probably other geographical names. The name has a connotation of a particular style of rod. The Philadelphia rod is a two-piece rod which can be extended to approximately 13 feet. The Chicago name is applied to rods with three or four sections which are placed together end to end. The San Francisco rod is similar to the "Philly" but it has two extensions. Rather than calling rods by a proper name, some people just call them "rods" or "storypoles."
A popular rod that doesn't seem to have a proper name is the telescoping rod. This rod is the rod of choice for field engineers working on projects where there is a great deal of change in elevation because telescoping rods are 25 or 30 feet long. Great rod lengths increase the elevation difference that can be transferred at one time. It has been argued that these types of rods wear rapidly; and, therefore, aren't as accurate as the more traditional rods. If telescoping rods are well cared for, they are excellent for construction use.
Rod Graduations
Level rods are graduated in feet, inches, and fractions; feet, tenths and hundredths; or meters and centimeters. The method of representing units of measurement onto the face of the rod also varies. The field engineer should, after studying the graduations on the face of the rod, be able to use any rod available. The illustration at the left shows the markings on a typical "engineer's rod" that is widely used on the construction site. Note that the rod is graduated to the nearest foot with large numbers which are usually painted red (thus the term "raise for red" when the instrument person cannot see the foot graduation). The feet are then graduated to the nearest tenth from 1 to 9. Each tenth is then graduated to the nearest one hundredth which is the width of the smallest mark on the rod.
To read the hundredths, the observer should keep in mind that the bottom of each graduation is an odd number and the top of each is an even number. Also, the longest graduation mark is for feet and tenths, which points upward. The next longest graduation is the half tenth or 0.05, 0.15, 0.25, etc., which points downward. The field engineer only has to learn to read the hundredths graduations of one tenth of the rod, because this pattern repeats itself for the length of the rod.
Metric rods are of various styles, and use different methods of graduation. One popular method is the "E" method of graduation, as seen in the illustration here, where the rod face is marked with alternat-ing left and right 10 centimeter (decimeter) "E's." At first glance, this looks difficult to read, however, with close examination and an understanding of metric measurement, it becomes apparent that reading the "E" method of graduation is quite simple.
Metric rods are read to the nearest centimeter and are estimated to the near-est millimeter. Once that is recognized, reading is simply observing the meters, the decimeters, and centimeters directly, and then estimating the millimeters. Note that the bottom of each "E" is an even decimeter, and the top of each "E" is half-way, or 5 centimeters. Each of the graduations on the rod represents one centimeter. For the example shown, the meters and decimeters are read directly as 0.8. The centimeters are then counted and found to be 9; so the reading is now 0.89. The millimeters are then estimated at 8, and added to the reading to obtain 0.898.