Briefing of Grade or level Instrument

A level is an optical instrument used to determine or verify points on the same horizontal plane in a process called leveling and is used in conjunction with a level to determine the relative height level of an object or mark.It is widely used in surveying,construction and other fields to measure height difference, transfer,measure and set the height of known objects or marks.It is also known as surveyor's level, builder's level,chunky level,or historically the "Y" level.It works by establishing a visual horizontal relationship between two or more points,for which a built-in telescope and a high-precision bubble level are used to achieve the necessary accuracy.Traditionally,the instrument was adjusted entirely by hand to ensure a level line of sight,but modern automatic versions self-compensate for small errors in the instrument's rough leveling and are therefore faster to use.Optical levels should not be confused with theodolites, which also measure angles in the vertical plane.

Describe 

The whole machine is usually installed on a tripod,and the telescope can freely rotate 360° on the horizontal plane.The surveyor adjusts the level of the instrument using the three precision leveling screws on the instrument via the tripod for coarse and fine adjustments so that the plane of rotation is level. Surveyors do this using a bull's-eye level built into the instrument holder.The surveyor looks through the eyepiece of the telescope while an assistant holds a vertical ruler graduated in inches or centimeters.The feet of the level meter are placed on the point where the level measurement needs to be performed. Rotate and focus the telescope until the horizontal ruler is clearly visible in the crosshairs.In the case of a tilt level,fine level adjustments are made via the height screw,using a high-precision bubble level fixed to the telescope.This can be seen through a mirror while adjusting, or the end of the bubble in a "split bubble" display can be seen inside a telescope.This also ensures accurate leveling of the telescope when photographing the line of sight.However,in the case of an automatic level, the height adjustment is done automatically by means of a suspended prism by gravity,as long as the coarse leveling of the base of the instrument is accurate within certain limits.When level,the staff graduation readings at the crosshairs and stadia marks are recorded,and an identifying mark or marker placed where the level staff rested on the object or position being surveyed.

Invention

In 1832, English civil engineer and inventor William Gravatt was commissioned to examine a proposed route for the South East Railway from London to Dover.Frustrated by the slow and cumbersome "Y" class of survey work, he designed a more portable,easier-to-use The "chunky" grade of the is named for its shorter appearance.The telescope of the historic "Y" spirit level is held in two brass arms that are part of the mount and can be easily removed to allow aiming inversion through 180 degrees or axial rotation of the telescope; both Both are used to compensate for optical alignment errors.Because the telescope is not fixed to the leveling mechanism, the "Y" instrument is assembled and disassembled for each aiming station.However, the chunky spirit level is permanently affixed to its two support arms and level mechanism,reducing measurement uncertainty and greatly reducing the time required to set up the instrument. Humpty uses the same horizontal aiming fundamentals.

Investigative actions

Main article:Leveling § Procedure

After careful setting of the spirit level,the height of the crosshair can be determined by aiming at a known datum of known height from a previous measurement or by using an arbitrary point with an assumed height.Aiming is done by an assistant surveyor who places a graduated staff vertically at the survey point.The surveyor rotates the telescope until the scale is in the crosshairs and records the reading.Repeat this for all sightings from that data. Move to another location within sight distance,relevel,and make a visual inspection of the known level from the previous measurement.This associates any new levels with previous levels.