Tilting levels
The tilting (or dumpy) levels require a two-step approach to setting them truly 'level'. The first is the coarse adjustment using the buble level on the base. Then they are fine adjusted using a tilting screw that angles the telescope with the accurate tubular level attached to it.
Depending on the instrument the tubular level is viewed directly using for example a mirror or both ends of the bubble are brought into coincidence using a prism. The more accurate geodetic levels can be 'reversed' (i.e. turned upside down) to cancel out any non-parallism between the telescope axis and the level. 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 tilting levels that I own are from Wild Heerbrugg are all designated 'N' for Nivellier 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).
