Selection key: This key is used to select the parameter to be changed, there are 4 LED tubes to display 4 codes, which represent the contents of the display. Bits 2-4 represent the parameter to be changed (2 is the hundredth digit of the value, 3 represents the tenth digit, 4 represents the first digit) The bright spot on the lower right leg of the LED tube represents the content that is now selected; it can be changed.