Oscilloscopes are laboratory instruments used to measure voltage against time and draw an instant graph of the voltage. They’re used for a multitude of applications, most commonly to test new electrical equipment. They’re one of the many instruments which need to be calibrated. They can display both alternating current AC and pulsating direct current DC wave forms from as low as 1Hz to several MHz. High-quality oscilloscopes can also display signal frequencies up to several hundred GHz.