In this, we will discuss hand level.
A hand level is a simple, compact instrument used for reconnaissance and preliminary survey, for locating contours on the ground, and for taking short cross-sections.
It consists of a rectangular or circular tube, 10 to 15 cm long, provided with a small bubble tube at the top. A line of sight, parallel to the axis of the bubble tube, is defined by a line joining a pin-hole at the eye end and a horizontal wire at the object end.
In order to view the bubble at the instant the object is sighted, a small opening, immediately below the bubble, is provided in the tube. The bubble is reflected through this opening on toa mirror, which is inside the tube inclined at 45° to the axis, and immediately under the bubble tube.
The mirror occupies half the width of the tube and the object is sighted through the other half. The line of sight is horizontal when the center of the bubble appears opposite the cross-wire or lies on a line ruled on the reflector.
2. How to Use?
To use the instrument
(I) Hold the instrument in hand (preferably against a rod or staff ) at the eye level and sight the staff kept at the point to be observed.
(II) Raise or lower the object end of the tube till the image of the bubble, seen in the reflector is bisected by the cross-wire.
(III) Take the staff reading against the cross-wire.
In some of the hand levels, a telescopic line of sight may also be provided.
3. Adjustment of the hand Level
To make the line of sight horizontal when the bubble is centered.
(1) Select two rigid supports P and Q at about 20 to 30 meters apart.
(2) Hold the level at a point A on the support at P and mark a point D on the other support Q, when the bubble is central.
(3) Shift the Instrument to Q, hold it at point D, center the bubble, and mark point B where the line of right strikes the first support. If A and B do not coincide, the instrument requires adjustment.
(4) Select a point C midway between A and B. With the adjustment screws, raise or lower the cross-wire till the line of sight bisects C.
|Read More: The Sextant|
|Read More: De Lisles Clinometer|