assemblies. The reticle has two cross hairs at rightangles to each other, and some models have stadiahairs. The telescope and level bar assembly ismounted on a spindle that permits the unit to berevolved only in a horizontal plane. It cannot beelevated or depressed. A clamp and tangent screwacts on this spindle for small motions to permitaccurate centering. The spindle mounts in afour-screw leveling head that rests on a foot plate.The foot plate screws onto the threads on thetripod. When the instrument is properly leveledand adjusted, the line of sight, defined by thehorizontal cross hair, will describe a horizontalplane.The two distinct types of engineer’s levels,classified according to their support, are the wyelevel and the dumpy level. The WYE LEVEL(fig. 11-24) is so called because its telescope issupported by a pair of wye rings. These rings canbe opened for the purpose of turning the telescopeor rotating it around its horizontal axis. Thebubble tube (vial) can be adjusted, either verticallyor laterally, by means of adjusting nuts at the endsof the bubble tube. All these features are providedfor the purpose of making fine adjustments. TheDUMPY LEVEL (fig. 11-25) has its telescoperigidly attached to the level bar, which supportsan adjustable, highly sensitive level vial. Duringvisual leveling operations and observations, bothtypes handle similar basic operations. Their crosshairs are brought into focus by rotation of theeyepiece, and their target, into clear focus byrotation of the focusing knob. Their telescope canbe exactly trained on targets by lightly tighteningthe azimuth clamp and manipulating the azimuthtangent screw.PRECISION LEVELOther types of leveling instruments have beenincorporated into the SEABEE units. In fact, theself-leveling level has now become standardFigure 11-24.-A wye level.11-28
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