A Surgical Electrocautery Unit (ESU), or diathermy machine, uses high-frequency alternating electrical current to generate heat, allowing surgeons to precisely cut tissue, coagulate (stop) bleeding, and ablate (destroy) unwanted tissue during surgery, enhancing efficiency and minimizing blood loss with tools like monopolar pencils or bipolar forceps. It converts standard power into specific waveforms for different effects (cut, coagulate, blend) and uses either a grounding pad (monopolar) or forceps (bipolar) to complete the circuit, with modes for various surgical needs.