Automatic levels

The automatic level uses an arrangement within the body of the instrument that sets the line of sight horizontal (perpendicular to gravity) automatically when the instrument is within a certain angle from being level. Often this is a prismatic arrangement. 

The instrument has only a single bubble level to bring the instrument to within the required degree of the true level for the automatic system to do its job. A number of level instruments are also equipped with a (coars) horizontal circle to allow measurement of horizontal angles with some accuracy. Depending on the instrument these are either in the 360 degree or 400 gon system (both representing a full circle).

Most of the automatic levels that I own are from Wild Heerbrugg are all designated 'NA' for Nivellier - Automatik and then depending on whether they have a horizontal circle a 'K' - Kreiss. The final number is then the series where the larger number is more accurate (a '1' serie is less accurate than a '2' etc).