Measuring instruments are available in various types for different applications, ranging from basic multimeters that measure electric current, voltage and resistance over several value ranges, to multifunction testing tools that offer a host of testing options. There are several specialised tools for specific purposes. Dataloggers record data specific to a location, over time, using instruments or sensors linked to digital processors. Electrical testing instruments, such as voltage and continuity checkers, electrical testers, continuity testers, cable locators and cable length measuring instruments, allow performing various checks to ascertain the proper functioning of electrical devices or to maintain the integrity of the system. A function generator produces electrical waveforms such as sine, square, sawtooth and triangular, in a wide range of frequencies, to test the functioning of equipment. Oscilloscopes analyse waveforms of electronic signals and display them as a function of time. A frequency counter measures the frequency in terms of oscillations or pulses per second. LCR meters measure the inductance, capacitance and resistance of a sensor or electronic component, to ensure its proper functioning. Logic analysers trigger, capture and display multiple signals from a digital circuit, and make explicit the timing relationships between signals in the system. Telecom and LAN measuring instruments, such as fiber optic testers and cable testers, detect errors in communication networks.