Specialized measuring instruments for measuring and evaluating electrical characteristics and electronic performance of electrical and electronic equipment. These instruments accurately measure electrical parameters such as voltage, current, resistance, impedance, frequency characteristics, insulation performance, and withstand voltage performance, and are used for product quality control and design verification. Includes digital multimeters, LCR meters, insulation resistance testers, withstand voltage testers, oscilloscopes, spectrum analyzers, and other equipment used for electronic component inspection, circuit board operation verification, and electrical equipment safety testing. This is a specialized electrical and electronic evaluation equipment field distinguished from physical dimension measurement and mechanical characteristic evaluation.