The use of level:
The use of leveling instrument includes the operation steps of instrument placement, rough leveling, aiming level, fine leveling and reading bai.
　　 One, place the level
Open the tripod and make the height moderate, visually estimate that the head of the frame is roughly level, check whether the legs of the tripod are placed firmly, and whether the telescopic screw of the tripod is tightened, then open the instrument case and take out the level, and place it on the head of the tripod to secure the instrument firmly with the connecting screw Attached to the tripod head.
　　 Two, rough leveling
　　Rough leveling is to center the bubble of the circular level so that the vertical axis of the instrument is roughly vertical, so that the collimation axis is roughly horizontal. During the leveling process, the moving direction of the bubble is the same as the moving direction of the left thumb.
　　 Three, aiming at the level ruler
　　 First, the eyepiece is aligned, that is, the telescope is pointed at a bright background, and the eyepiece is rotated to focus the light spiral to make the crosshair clear. Loosen the brake screw again, turn the telescope, aim at the level ruler with the sight and sight on the telescope tube, and tighten the brake screw. Then observe from the telescope; turn the animal lens to align the light spiral to make the target clear, and then turn the micro-motion spiral to align the vertical wire with the level ruler.
　　 When the eyes move slightly up and down on the end of the eyepiece, if you find that the crosshairs move relative to the target image, this phenomenon is called parallax. The reason for the parallax is that the target imaging plane and the crosshair plane do not coincide. Since the existence of parallax will affect the accuracy of the reading, it must be eliminated. The method of elimination is to re-focus the objective lens carefully until the eyes move up and down and the reading does not change. At this time, the images of the crosshairs and the target are very clear from the end of the eyepiece.
　　Four, precision and reading
　　 The eye looks at the bubble in the vial through the bubble observation window located on the left of the eyepiece, and turns the slightly inclined spiral with the right hand to make the images at both ends of the bubble match, which means that the collimation axis of the level is accurately level. At this time, you can use the middle wire of the crosshair to read on the ruler. Today's leveling instruments mostly use inverted image telescopes, so the reading should start from small to large, that is, read from top to bottom. Estimate the number of millimeters first, and then report all the readings. Although fine-leveling and reading are two different operating steps, in the implementation of leveling, the two operations are regarded as a whole; that is, read after fine-leveling, and after reading, check whether the tube level bubbles are fully consistent. Only in this way can accurate readings be obtained.
　　 In order to unify the national elevation system and meet the needs of various surveys, surveying and mapping departments have buried and measured many elevation points throughout the country. These points are called Bench Marks, abbreviated as BM. Leveling usually refers to the elevation of other points from the benchmarking point. There are two types of benchmarks: permanent and temporary. National level benchmarking points are generally made of stone or reinforced concrete and are buried deep below the ground freezing line. There is a hemispherical sign made of stainless steel or other non-corrosive materials on the top surface of the marker. Some leveling points can also be set on a stable wall foot, called wall leveling points.
　　 Permanent benchmarking points on construction sites are generally made of concrete or reinforced concrete. Temporary benchmarking points can be driven into the ground with hard rocks protruding from the ground or large wooden piles, and the top nails are hemispherical iron nails.
After the leveling points are buried, a diagram of the relationship between the leveling points and nearby fixed buildings or other features should be drawn. The number and elevation of the leveling points should also be written on the map, which is called a note of the point, so that you can find the location of the leveling point in the future. For use. BM is usually added before the number of the level point as the code name of the level point.
　　The main forms of leveling route are: closed leveling route, attached leveling route and branched leveling route.
　　 When the elevation point to be measured is far from the benchmark point or the elevation difference is large, it is necessary to install the instrument multiple times to measure the elevation difference between the two points. To measure the height difference between points A and B, intermediate points such as 1, 2, 3, 4, ... are added to the AB line, and the AB height difference is divided into several leveling stations. The middle point is only used to transmit the height, and is called Turning Point, abbreviated as TP. There is no fixed mark for the turning point, and there is no need to calculate the elevation. Obviously, every time the instrument is installed, a height difference can be measured.