Bull's eye level

Bull's eye levels are used primarily by carpenters in construction, but can also be found as features of compasses or other devices that need to be kept from tipping in certain directions (whether it be for functionality or precision of measurements).

Small bull's eye levels are also found incorporated into tripods.

Another name for a bull's eye level is a "circular bubble" which is the name used by surveyors in the United Kingdom.

[1] The device was unique in that it could be placed on a machine bed and show tilt on x and y axes simultaneously; eliminating the need to rotate the level 90 degrees.

Production restarted in 1980s by Thomas Butler Technology, Rockford, Illinois, but finally ended in the mid 1990s.