A chronoscope or time viewer is a device that uses images that show past or future events like a television. They can sometimes also cause time travel. They are common in sci-fi, and often take different forms. Some act like cameras recording past and future events and showing what an object would look like in a different time period. Others are more like TVs and show videos and visions of the past and future. Chronoscopes are often used as plot devices, as they can often reveal various details that are necessary for the plot. Examples of Chronoscope include: