The difference between these two readings equals the change in elevation, which is why this method is also called differential levelling. The rod is then held on an unknown point and a reading is taken in the same manner, allowing the elevation of the new (foresight) point to be computed. This gives the height of the instrument above the starting (backsight) point and allows the height of the instrument (H.I.) above the datum to be computed. A rod or staff is held vertical on that point and the instrument is used manually or automatically to read the rod scale. Set up the instrument within 100 metres (110 yards) of a point of known or assumed elevation. The level line of sight is 2.Ī typical procedure for a linear track of levels from a known datum is as follows. When level, the staff graduation reading at the crosshairs is recorded, and an identifying mark or marker placed where the level staff rested on the object or position being surveyed.ĭiagram showing relationship between two level staff, or rods, shown as 1 and 3. However, in the case of an automatic level, altitude adjustment is done automatically by a suspended prism due to gravity, as long as the coarse levelling is accurate within certain limits. This can be viewed by a mirror whilst adjusting or the ends of the bubble can be displayed within the telescope, which also allows assurance of the accurate level of the telescope whilst the sight is being taken.
STICK RANGER WIKI LEVEL MANUAL
In the case of a high accuracy manual level, the fine level adjustment is made by an altitude screw, using a high accuracy bubble level fixed to the telescope. The telescope is rotated and focused until the level staff is plainly visible in the crosshairs. The level staff is placed vertically using a level, with its foot on the point for which the level measurement is required. The surveyor looks through the eyepiece of telescope while an assistant holds a vertical level staff which is a graduated in inches or centimeters. The surveyor does this with the use of a bull's eye level built into the instrument mount. The surveyor adjusts the instrument's level by coarse adjustment of the tripod legs and fine adjustment using three precision levelling screws on the instrument to make the rotational plane horizontal. The complete unit is normally mounted on a tripod, and the telescope can freely rotate 360° in a horizontal plane. The cross hairs are used to establish the level point on the target, and the stadia allow range-finding stadia are usually at ratios of 100:1, in which case one metre between the stadia marks on the levelling staff represents 100 metres from the target. Optical levelling employs an optical level, which consists of a precision telescope with crosshairs and stadia marks. The distance between the marks is 155 mm, yielding a distance to the rod of 15.5 m. The top mark is at 1500 mm and the lower is at 1345 mm. Stadia marks on a crosshair while viewing a metric levelling rod.
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