Figure 11-19.-Vertical angles from zenith distances (mils).last zero dropped. The auxiliary scales are graduatedfrom 0 to 10 roils in 0.2-mil increments. Readings onthe auxiliary scale can be interpolated to 0.1 mil.The vertical circle reads 0 mil when the telescopeis pointed at the zenith, and 3,200 mils when it is pointedstraight down. A level line reads 1,600 roils in the directposition and 4,800 roils in the reverse. The values readare zenith distances. These zenith distances can beconverted into vertical angles as shown in figure 11-19.One-Second TheodoliteThe 1-sec theodolite is a precision directiontype of instrument for observing horizontal andvertical directions. This instrument is similar to,45.632Figure 11-20.-A 1-second theodolite.11-24
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