This is a RS232C interface tester called "Quick Test Plus" from Black Box. It displays the status of the RS232C interface signal lines with LEDs, allowing for easy diagnosis. You can check the pin assignments and the status of each signal (TD, RD, RTS, CTS, etc.). It's a useful tool for troubleshooting data communication problems. It can be used to check the connection of communication devices and to check for cable breaks. The operation has not been confirmed before listing due to lack of an environment. Please purchase only if you understand and accept this. RS232c, conversion connector, D-SUB 9-pin/25-pin