- The simplest type is the Dumpy Level in Land Surveying,the basic components of which are:-
- A tripod upon which the instrument is attached for use.
- A tribach, or alternatively a ball and socket, which is used to bring the telescope into a near horizontal position.
- In dumpy Level, A telescope, fitted with a diaphram on which cross-hairs are etched to define the line of sight.
- A bubble tube, attached to the telescope tube, and used to determine when the line of sight is horizontal.
Tripod
The tripod consists of three pointed legs, (wooden or metal), with a solid metal head. The legs may be rigid or telescopic.
For good leveling it is essential that there be no movement or free-play in any of the joints. The metal feet on the legs, the sliding joints of telescopic legs and the hinged attachments
to the head should be checked and adjusted regularly.
Wooden legs should be painted at least once each six months with a 50/50 mixture of linseed oil and turpentine.
Tribach
The tribach consists of two plates (one upper – the other lower) joined by three adjustable foot- screws.
The tribach is permanently fixed to the telescope and its axis, in such a way that the upper plate is parallel to the telescope tube.
The three foot screws are manipulated to bring the upper plate and the telescope into a horizontal position.
The tribach may be screwed onto the head of the tripod, or alternatively a central screw within the tripod head may be screwed into the base of the tribach.
For “quickset” levels the three screw tribach is replaced by a ball and socket unit which performs the same function.
The upper plates of tribachs or ball and socket units may be fitted with a small pea, or centre bubble, so that quick approximate setting up of the instrument can be carried out.
The tribach should fit firmly to the tripod head with no free-play and there should be no sloppiness in the movement of foot-screws. A protector for the tripod head screws is provided and should always be used. Foot screws should be kept free of dust and lightly oiled with fine oil as required.