![]() ![]() While taking observations, if the vertical circle of the instrument is on left side of the observer, the instrument is said to face left and the readings taken in this position are known as face left readings. It is the process of rotating the telescope of the theodolite 180° about the vertical axis in horizontal plane. ![]() It is also known as plunging or reversing. It means to bring the telescope upside down for pointing in opposite direction by 180° revolution of the telescope about horizontal axis in vertical plane. ![]() It is the process of setting theodolite exactly over the station using a plumb bob. The following terms should be remembered while dealing with a transit theodolite 1)Centering: Micrometer theodolite is that type of theodolite in which micrometer is provided for reading out graduated circle. Vernier theodolite is the type of theodolite in which the graduated circle is read with the help of Vernier. This type of theodolite is obsolete now.įigure 2: Non-transit theodolite. If the telescope of a theodolite cannot be revolved about the trunnion axis, it is known as a non-transit theodolite. This type of theodolite is commonly used for surveying. If line of sight of the telescope can be reversed through the rotation of telescope by 180° about the trunnion axis in vertical plane, the theodolite is known as transit theodolite. There are basically two classifications of theodolite 1)Transit Theodolite: It is considered to be more precise and speedy than the regular chain survey, compass or plane-table surveying and is commonly used in engineering fields for land surveying, route surveying and constructional surveys. It can completely rotate along the horizontal plane and its telescope can be rotated up to 180°. Precisely machined and balanced bobs have pointed tips, and can be made of brass, steel, or other materials, including plastic.In survey, a theodolite is an instrument mounted with a moveable telescope, used for precise measurements of horizontal and vertical angles. (Masons prefer nylon because it stands up better over time to the dampness that comes with the trade.) At one end of the string the weight is affixed. The plumb consists of a specially designed weight and coarse string made of twisted cotton or nylon threads. In a sense, the plumb bob is the vertical equivalent of the line level. ![]() You don’t have to be a physics whiz to understand that a string suspended with a weight at the bottom will be both vertical and perpendicular to any level plane through which it passes. The plumb bob or plumb line employs the law of gravity to establish what is “plumb” (that is, what is exactly vertical, or true). As is so often the case, it isn’t how fancy the tool is, but how well you use it. For most home toolboxes, I recommend having a single bob that weighs a few ounces. (It’s also thought that, in tandem, they used flooded ditches to determine levels.) Plumb bobs may weigh as little as an ounce or as much as several pounds, depending upon the application. Evidence suggests that Egyptian architects used plumb bob-like tools to establish verticals in constructing the pyramids. ![]()
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