# A spirit level depends on the temperature

A spherometer is a measuring device for determining the radii of curvature of spherical lenses. It essentially consists of a flat hollow cylinder on which the lens can be placed centrally. In the center of the hollow cylinder there is a measuring sensor with which the lowering or curvature can be determined relative to the zero position. The zero position can be set by placing a plane-parallel plate on the spherometer and using it to calibrate the measuring probe.
The radius of curvature can be calculated from the measured depression or curvature and the inner or outer diameter of the ring. According to the Pythagorean theorem:

Our spherometers

Source: www.wikipedia.de

The Spirit level (also level, level or mason's level) is a tool for checking the horizontality or verticality of an object and consists of a mounted bubble level that is aligned with one or more precise measuring surfaces.
Originally, the term spirit level referred to a contained dragonfly that is not much larger than this dragonfly and has a flat sole. Because of its brevity, it can only be used to check individual objects such as beams or stone blocks for horizontality. In order to be able to check composite structures, such as a wall or paving, this 'spirit level' was placed on a straightedge. The slope of a canal or paving can be checked by measuring or by experience with the point at which the dragonfly enters. A mark on the left and right of the level that corresponds to a deviation of one degree is common.
Level, level, also a mason's level (as a tool of the mason), describes a tool with one or two vials (more are possible), which are in a 30–200 cm long profile made of aluminum, water-resistant, stable hardwood, cast aluminum, plastic or the like. are embedded with one or two measuring surfaces. These measuring surfaces can be milled or coated. With two vials, these are installed perpendicular to each other so that both the horizontal and the vertical can be checked. There are also levels with three dragonflies; the third vial is then provided for checking the 45 ° inclination.
Nowadays, masonry scales of various lengths are almost exclusively made with two dragonflies and these are generally referred to as spirit levels.

Special designs

Spirit level with three dragonflies
While the spirit level is actually a tool that can only be used to install individual components, e.g. B. stones, bricks, pipes, beams and not used to measure buildings over longer distances, there are other forms such as the cord spirit level, post spirit level or the laser spirit level.
The cord spirit level is a mounted dragonfly with two eyelets, so that you can put it in a cord, e.g. B. a batter board can knot. Due to the sagging of a horizontal cord and the susceptibility to wind and vibrations, this can only be used as a rough guide. The line spirit level should hang as precisely as possible in the middle and the line should be kept very tight.

The Laser level has a laser whose beam is offset by a few centimeters in height and shines parallel to the sole of the spirit level.
A laser unit consisting of a laser diode, control electronics and a lens for aligning and focusing the laser beam is built into the profile of a spirit level. The laser beam is then adjusted to the measuring surface of the spirit level. The accuracy of the laser level essentially depends on the individual accuracy and the interaction of the individual components of the level, level profile and laser unit. Professional laser spirit levels achieve an accuracy of 0.25 mm / m and have vials with much higher sensitivity than normal spirit levels with 0.5 mm / m.
Cheap laser spirit levels from the discounter often have poorer accuracies (more than 1 mm / m) or do not even have an accuracy specification. In addition, there are poorly installed and insufficiently adjusted laser units or vials.
To transmit a height, e.g. B. a meter plan, there are laser levels with a leveling plate that can be set up on a tripod or other fixed position. While a hose level or level can only be used by two workers, one worker can transfer a height with a laser level.
The range of the laser beam depends heavily on the ambient brightness and the wavelength of the laser diode. Good laser spirit levels have a range of 30–40 m under normal construction site conditions. For greater ranges and accuracy, a leveling device or laser level should be used.
Measurement accuracy
The Measurement accuracy is usually indicated on the spirit level in mm / m, but also in degrees and is confirmed by an official test office with a seal. It only describes the maximum measurement error for measuring over a distance with the length of the respective spirit level and not for checking two points with a distance of a few cm and also not for a measurement with intermediate points, e.g. B. at a distance of 1 m with a spirit level with a length of 40 cm.
The measuring accuracy depends on the quality of the vial, the installation accuracy, the aluminum profile / wooden body and the accuracy of the setting edge. It can deteriorate due to improper handling (impacts, loads, extreme temperatures and especially with wooden spirit levels due to moisture or even wetness), incorrect storage, insufficient care or aging.
Usual measuring accuracies in normal position when new:

• 0.057 °, this corresponds to 1 mm / m
• 0.0285 °, this corresponds to 0.5 mm / m

If you are using a certain spirit level for the first time, you can convince yourself by placing it on a horizontal plane and rotating around a semicircle that the spirit level has not become inaccurate: the display must not change. (Otherwise it is said that the spirit level “lies”). This procedure of a checking control measurement with a measuring device placed in the opposite direction is also recommended for important leveling.
slang
To stand / be in the water. When it says in technical jargon that an object is in the water (or: is in the water), then that means that the object is horizontal or vertical.

history

Principle of the ancient level
The ancient Egyptians already used an oversized spirit level to build the pyramid base plate, by drawing a rectangular trench around the planned construction site and filling it with water. Everything that was above the waterline between the canals has been removed. It is said that accuracies of 2 cm were achieved in this way.
In ancient times, an equilateral triangle was used as a level, in which a plumb line was hung. The plumb line points to the center of the base of the triangle when it is level.

Source: www.wikipedia.de

The caliper is a length measuring device.
The vernier caliper has two measuring arms for measuring external and internal dimensions. In addition, it usually has a depth measuring rod that is used to measure z. B. holes is used. The classic design of the caliper has a vernier to increase the reading accuracy. Variants in which the measured value can be read off a round dial are also used. In the meantime, however, calipers with a digital numeric display are almost exclusively used. Although these do not have a higher measurement accuracy, they are easier to read. It is also possible to transfer the measurement data to the computer for evaluation.
Since the vernier caliper is a measuring device and not a gauge, the previously used terms calliper or caliper in training for technical professions have been replaced by the term vernier caliper. Even earlier, the term "caliber" was used colloquially, especially in southern Germany. However, the word vernier caliper can only slowly gain acceptance in everyday language.
Most calipers have a table on the back that shows the size of the drill hole for tapping. However, some tables are not up to date. The drill hole diameter up to M8 should be calculated with the rule of thumb 0.8 times the thread diameter.
In contrast to the micrometer, the vernier caliper does not adhere to the abbe comparator principle. The tilting error of the 1st order caused by this leads to a measurement inaccuracy that is fundamentally unavoidable due to the structure of the caliper. Other possible errors are parallax, guidance errors, system errors on the object to be measured and wear (damage, contamination).
Measuring with the vernier caliper is a direct measurement method, since the input and output variables are identical (in this case the length).
Advantages of the caliper compared to other measuring devices are:

• robust construction
• quick measurement possible
• Vernier calipers are inexpensive
• Vernier calipers are easy to use
• Vernier calipers can be used mobile

• With calipers, the measurement uncertainty is greater than the resolution of the display.

Typical structure of a caliper

• fixed measuring arm
• movable measuring arm
• knife-edge measuring surfaces
• Measuring surfaces for outside measurements
• Slider
• Vernier
• Locking device
• Rail with main division
• Depth gauge
• Measuring surfaces for depth measurement

Types of calipers

• Precision pocket caliper with linear scale and vernier
• Precision workshop caliper with linear scale
• Vernier caliper with round scale
• Digital precision caliper (capacitive measuring system)
• Digital workshop caliper with LCD display and fine adjustment device
• Precision tooth measuring caliper
• Depth caliper
• Height caliper

Calipers can be read from a clock or a vernier.

Source: www.wikipedia.de