The most basic function of electronic components is to block the flow of current. The two most basic parameters for measuring resistors are resistance and power. The resistance value is used to indicate the resistance of the resistor to the current, expressed in ohms. In addition to the basic units, there are kiloohms and megaohms. Power is used to indicate the maximum current that the resistor can withstand. It is expressed in watts. There are many kinds, such as 1 / 16W, 1 / 8W, 1 / 4W, 1 / 2W, 1W, 2W, etc. if the maximum value is exceeded, the resistor will burn out. According to the manufacturing materials of resistors, there are cement resistors (low manufacturing cost, high power, high thermal noise, inaccurate resistance value and unstable operation), carbon film resistors, metal film resistors (small volume, stable operation, low noise and high accuracy), metal oxide film resistors, etc. According to whether the resistance value is variable, it can be divided into fine-tuning resistance, adjustable resistance, potentiometer, etc.