2. Instrument

a. Level Instrument

A Level is a telescope-based surveying instrument used to establish elevations. It has a gravity-based provision, a bubble, to orient the telescope.

Figure A-2 Different Level Instruments

b. Instrument Set Up

On a perfectly adjusted level, the Line of Sight (LoS) is perpendicular to the instrument's Vertical Axis (VA). When an instrument's bubble is centered, the VA coincides with a vertical line and the LoS is horizontal, Figure A-3.

Figure A-3 Properly Oriented Level

At the instrument location, a horizontal line and level line coincide, Figure A-4. The further from the instrument, the greater the lines' separation.

Figure A-4 Instrument Setup