page_title: Analog computer
section_title: Precursors
hierarchical_section_title: Analog computer / Timeline of analog computers / Precursors
caption_attribution_description: Français&#160;: Fragment principal de la machine d'Anticythère. Le mécanisme consiste en un système complexe de 32 roues et plaques portant des inscriptions relatives aux signes du zodiaque et aux mois. L'étude des fragments suggère qu'il s'agissait d'une sorte d'astrolabe utilisée pour la navigation maritime. L'interprétation désormais généralement acceptée remonte aux études du professeur Derek de Solla Price, qui fut le premier à suggérer que le mécanisme est une machine à calculer le calendrier solaire et lunaire, c'est-à-dire une machine ingénieuse pour déterminer le temps sur la base des mouvements du soleil et de la lune, leur relation (éclipses) et les mouvements des autres étoiles et des planètes connues à cette époque. Le mécanisme fut probablement construit par un mécanicien ingénieux de l'école de Poséidonios à Rhodes. Cicéron, qui visita l'île en 79/78 a. C. rapporte que de tels engins étaient en effet conçus par le philosophe stoïcien Poséidonios d'Apamée. La conception du mécanisme d'Anticythère paraît suivre la tradition du planétarium d'Archimède, et peut être reliée aux cadrans solaires. Son mode opératoire est basé sur l'utilisation de roues dentées. La machine est datée de 89 avant J.-C. environ et provient de l'épave trouvée au large de l'île d'Anticythère. Musée archéologique national, Athènes, n°15987. Español: Fragmento principal de la máquina de Anticitera. El mecanismo consiste en un sistema complejo de 32 ruedas y placas con inscripciones relativas a los signos del zodiaco, meses, eclipses y juegos pan-Helénicos. El estudio de los fragmentos sugiere que se trataba de una especie de astrolabio utilizado para la navegación marítima. La interpretación más aceptada procede de los estudios del profesor Derek de Solla Price, que fue el primero en sugerir que el mecanismo es una calculadora del calendario solar y lunar, es decir, una máquina ingeniosa para determinar el tiempo basándose a los movimientos del sol y de la luna, su relación (eclipses) y los movimientos de otros planetas y estrellas conocidos en esa época. El mecanismo fue construido, probablemente, por un ingeniero mecánico de la escuela de Poséidonios en Rhodes. Cicerón, quien visitó la isla en el 79/78 a. C., cuenta que tales ingenios fueron, en efecto, concebidos por el filósofo Poseidonios de Apamea. La concepción del mecanismo de Anticitera parece seguir la tradición del planetario de Arquímedes, y puede estar relacionado con los cuadrantes solares. Su funcionamiento está basado en el uso de ruedas dentadas. La máquina data del 89 a. C. aproximadamente, y proviene del naufragio encontrado en la isla de Anticitera. Museo Arqueológico Nacional, Atenas, n°15987. English: Main w:en:Antikythera mechanism fragment (fragment A). The mechanism consists of a complex system of 30 wheels and plates with inscriptions relating to signs of the zodiac, months, eclipses and pan-Hellenic games. The study of the fragments suggests that this was a kind of astrolabe. The interpretation now generally accepted dates back to studies by Professor w:en:Derek de Solla Price, who was the first to suggest that the mechanism is a machine to calculate the solar and lunar calendar, that is to say, an ingenious machine to determine the time based on the movements of the sun and moon, their relationship (eclipses) and the movements of other stars and planets known at that time. Later research by the Antikythera Mechanism Research Project and scholar Michael Wright has added to and improved upon Price's work. The mechanism was probably built by a mechanical engineer of the school of Posidonius in Rhodes. Cicero, who visited the island in 79/78 B.C. reported that such devices were indeed designed by the Stoic philosopher Posidonius of Apamea. The design of the Antikythera mechanism appears to follow the tradition of Archimedes' planetarium, and may be related to sundials. His modus operandi is based on the use of gears. The machine is dated around 89 B.C. and comes from the wreck found off the island of Antikythera. National Archaeological Museum, Athens, No. 15987.
context_page_description: An analog computer or analogue computer is a type of computer that uses the continuously changeable aspects of physical phenomena such as electrical, mechanical, or hydraulic quantities to model the problem being solved. In contrast, digital computers represent varying quantities symbolically and by discrete values of both time and amplitude.
  Analog computers can have a very wide range of complexity. Slide rules and nomograms are the simplest, while naval gunfire control computers and large hybrid digital/analog computers were among the most complicated. Systems for process control and protective relays used analog computation to perform control and protective functions.
  Analog computers were widely used in scientific and industrial applications even after the advent of digital computers, because at the time they were typically much faster, but they started to become obsolete as early as the 1950s and 1960s, although they remained in use in some specific applications, such as aircraft flight simulators, the flight computer in aircraft, and for teaching control systems in universities.
context_section_description: This is a list of examples of early computation devices considered precursors of the modern computers. Some of them may even have been dubbed as 'computers' by the press, though they may fail to fit modern definitions.
  The Antikythera mechanism was an orrery and is considered an early mechanical analog computer, according to Derek J. de Solla Price. It was designed to calculate astronomical positions. It was discovered in 1901 in the Antikythera wreck off the Greek island of Antikythera, between Kythera and Crete, and has been dated to c. 100 BC during the Hellenistic period of Greece. Devices of a level of complexity comparable to that of the Antikythera mechanism would not reappear until a thousand years later.
  Many mechanical aids to calculation and measurement were constructed for astronomical and navigation use.
  The planisphere was first described by Ptolemy in the 2nd century AD. The astrolabe was invented in the Hellenistic world in either the 1st or 2nd centuries BC and is often attributed to Hipparchus. A combination of the planisphere and dioptra, the astrolabe was effectively an analog computer capable of working out several different kinds of problems in spherical astronomy. An astrolabe incorporating a mechanical calendar computer and gear-wheels was invented by Abi Bakr of Isfahan, Persia in 1235. Abū Rayhān al-Bīrūnī invented the first mechanical geared lunisolar calendar astrolabe, an early fixed-wired knowledge processing machine with a gear train and gear-wheels, c. AD 1000. The castle clock, a hydropowered mechanical astronomical clock invented by Al-Jazari in 1206, was the first programmable analog computer.
  The sector, a calculating instrument used for solving problems in proportion, trigonometry, multiplication and division, and for various functions, such as squares and cube roots, was developed in the late 16th century and found application in gunnery, surveying and navigation.
  The planimeter was a manual instrument to calculate the area of a closed figure by tracing over it with a mechanical linkage.
  The slide rule was invented around 1620–1630, shortly after the publication of the concept of the logarithm.  It is a hand-operated analog computer for doing multiplication and division. As slide rule development progressed, added scales provided reciprocals, squares and square roots, cubes and cube roots, as well as transcendental functions such as logarithms and exponentials, circular and hyperbolic trigonometry and other functions. Aviation is one of the few fields where slide rules are still in widespread use, particularly for solving time–distance problems in light aircraft.
  In 1831–1835, mathematician and engineer Giovanni Plana devised a Perpetual Calendar machine, which, though a system of pulleys and cylinders and over, could predict the perpetual calendar for every year from AD 0 (that is, 1 BC) to AD 4000, keeping track of leap years and varying day length.
  The tide-predicting machine invented by Sir William Thomson in 1872 was of great utility to navigation in shallow waters. It used a system of pulleys and wires to automatically calculate predicted tide levels for a set period at a particular location.
  The differential analyser, a mechanical analog computer designed to solve differential equations by integration, used wheel-and-disc mechanisms to perform the integration. In 1876 James Thomson had already discussed the possible construction of such calculators, but he had been stymied by the limited output torque of the ball-and-disk integrators. In a differential analyzer, the output of one integrator drove the input of the next integrator, or a graphing output. The torque amplifier was the advance that allowed these machines to work. Starting in the 1920s, Vannevar Bush and others developed mechanical differential analyzers.
caption: The Antikythera mechanism, dating between 150 and 100 BC, was an early analog computer.
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