Query: When the measuring equipment gets old and needs replacing, it often requires re-calibration.

Relevant passages:
Load cell <=SEP=> A load cell is a transducer that is used to create an electrical signal whose magnitude is directly proportional to the force being measured . The various types of load cells include hydraulic load cells , pneumatic load cells and strain gauge load cells .

Microphone <=SEP=> A microphone , colloquially nicknamed mic or mike ( -LSB- ˈmaɪk -RSB- ) , is a transducer that converts sound into an electrical signal .   Microphones are used in many applications such as telephones , hearing aids , public address systems for concert halls and public events , motion picture production , live and recorded audio engineering , sound recording , two-way radios , megaphones , radio and television broadcasting , and in computers for recording voice , speech recognition , VoIP , and for non-acoustic purposes such as ultrasonic sensors or knock sensors .   Several different types of microphone are in use , which employ different methods to convert the air pressure variations of a sound wave to an electrical signal . The most common are the dynamic microphone , which uses a coil of wire suspended in a magnetic field ; the condenser microphone , which uses the vibrating diaphragm as a capacitor plate , and the piezoelectric microphone , which uses a crystal of piezoelectric material . Microphones typically need to be connected to a preamplifier before the signal can be recorded or reproduced .

Heat flux sensor <=SEP=> A heat flux sensor is a transducer that generates an electrical signal proportional to the total heat rate applied to the surface of the sensor . The measured heat rate is divided by the surface area of the sensor to determine the heat flux .   The heat flux can have different origins ; in principle convective , radiative as well as conductive heat can be measured . Heat flux sensors are known under different names , such as heat flux transducers , heat flux gauges , heat flux plates . Some instruments that actually are single-purpose heat flux sensors like pyranometers for solar radiation measurement . Other heat flux sensors include Gardon gauges ( also known as a circular-foil gauge ) , thin-film thermopiles , and Schmidt-Boelter gauges . In SI units , the heat rate is measured in Watts , and the heat flux is computed in Watts per meter squared .

Sound reinforcement system <=SEP=> A sound reinforcement system is the combination of microphones , signal processors , amplifiers , and loudspeakers in speaker cabinets all controlled by an audio mixing board that makes live or pre-recorded sounds louder and may also distribute those sounds to a larger or more distant audience . In many situations , a sound reinforcement system is also used to enhance or alter the sound of the sources on the stage , typically by using electronic effects , such as reverb , as opposed to simply amplifying the sources unaltered .   A sound reinforcement system for a rock concert in a stadium may be very complex , including hundreds of microphones , complex live sound mixing and signal processing systems , tens of thousands of watts of amplifier power , and multiple loudspeaker arrays , all overseen by a team of audio engineers and technicians . On the other hand , a sound reinforcement system can be as simple as a small public address ( PA ) system , consisting of , for example , a single microphone connected to a 100 watt amplified loudspeaker for a singer-guitarist playing in a small coffeehouse . In both cases , these systems reinforce sound to make it louder or distribute it to a wider audience .   Some audio engineers and others in the professional audio industry disagree over whether these audio systems should be called sound reinforcement ( SR ) systems or PA systems . Distinguishing between the two terms by technology and capability is common , while others distinguish by intended use ( e.g. , SR systems are for live event support and PA systems are for reproduction of speech and recorded music in buildings and institutions ) . In some regions or markets , the distinction between the two terms is important , though the terms are considered interchangeable in many professional circles .

Surveying <=SEP=> Surveying or land surveying is the technique , profession , and science of determining the terrestrial or three-dimensional position of points and the distances and angles between them . A land surveying professional is called a land surveyor . These points are usually on the surface of the Earth , and they are often used to establish land maps and boundaries for ownership , locations like building corners or the surface location of subsurface features , or other purposes required by government or civil law , such as property sales .   Surveyors work with elements of geometry , trigonometry , regression analysis , physics , engineering , metrology , programming languages and the law . They use equipment like total stations , robotic total stations , GPS receivers , retroreflectors , 3D scanners , radios , handheld tablets , digital levels , subsurface locators , drones , GIS and surveying software .   Surveying has been an element in the development of the human environment since the beginning of recorded history . The planning and execution of most forms of construction require it . It is also used in transport , communications , mapping , and the definition of legal boundaries for land ownership . It is an important tool for research in many other scientific disciplines .