In astronomy, geography, and related sciences and contexts, a direction or plane passing by a given point is said to be vertical if it contains the local gravity direction at that point.
Conversely, a direction, plane, or surface is said to be horizontal (or leveled) if it is everywhere perpendicular to the vertical direction.
A theodolite (/θiˈɒdəˌlaɪt/) is a precision optical instrument for measuring angles between designated visible points in the horizontal and vertical planes. The traditional use has been for land surveying, but it is also used extensively for building and infrastructure construction, and some specialized applications such as meteorology and rocket launching.
It consists of a moveable telescope mounted so it can rotate around horizontal and vertical axes and provide angular readouts. These indicate the orientation of the telescope, and are used to relate the first point sighted through the telescope to subsequent sightings of other points from the same theodolite position. Depending on the instrument, these angles can be measured with accuracies down to microradians or seconds of arc. From these readings a plan can be drawn, or objects can be positioned in accordance with an existing plan. The modern theodolite has evolved into what is known as a total station where angles and distances are measured electronically, and are read directly to computer memory.
In navigation, bearing or azimuth is the horizontal angle between the direction of an object and north or another object. The angle value can be specified in various angular units, such as degrees, mils, or grad. More specifically:
An overline, overscore, or overbar, is a typographical feature of a horizontal line drawn immediately above the text. In old mathematical notation, an overline was called a vinculum, a notation for grouping symbols which is expressed in modern notation by parentheses, though it persists for symbols under a radical sign. The original use in Ancient Greek was to indicate compositions of Greek letters as Greek numerals. In Latin, it indicates Roman numerals multiplied by a thousand and it forms medieval abbreviations (sigla). Marking one or more words with a continuous line above the characters is sometimes called overstriking, though overstriking generally refers to printing one character on top of an already-printed character.
An overline, that is, a single line above a chunk of text, should not be confused with the macron, a diacritical mark placed above (or sometimes below) individual letters. The macron is narrower than the character box.
A water level (Greek: Aλφαδολάστιχο or (υδροστάθμη) [Alfadolasticho]) is a siphon utilizing two or more parts of the liquid water surface to establish a local horizontal line or plane of reference. It is used to determine the apparent inclination of an object or surface and for matching water level elevations at locations that are too far apart for a spirit level to span.
The simplest water level is a section of clear tubing, partially filled with water. Water is easily procured for use, and easily discarded after use. The ends are held vertical, and the rest of the tubing lies on the ground or floor. The water level at each end of the tube will be at the same elevation, whether the two ends are adjacent or far apart, so a line between them will be horizontal at its midpoint and a shed base, building foundation or similar structure laid out using several such lines will be "horizontal" within building tolerances on any scale over which use of a water level is practicable. Water levels have been used for many years. The water level is lower-tech than the laser level, but it can be more accurate over long distances, and works without a sightline, such as around corners. To avoid error, all of the water should be at the same temperature. Other sources of error include difficulty reading due to meniscus.