We own a very rare Zeiss level.

It is possible to transfer a horizontal level over a distance of 1.000 m with an accuracy of 2 mm. It can also measure the horizontal angle of an object.

This side shows the very complex bubble for adjusting the horizontal level. A small mirror reflects the daylight into a prisma. This prisma devides the large airbubble in two parts and both are presented in mirror view. When the bubble halfs are in line, the instrument is exactly horizontal.

Schematic view of the split bubble.