Exposure meter during photography

Modern cameras are equipped with exposure (photometry) meters, which measure and adjust shooting conditions (aperture size, shutter speed and whether the flash is on or off) according to the light in the shooting environment. There is also manual adjustment to adjust the shooting conditions with the exposure meter. It is said that the early cameras did not have a built-in exposure (photometry) instrument, but used another exposure (photometry) instrument to measure the light of the shooting environment, which would be displayed according to the shooting conditions, and then the photographer set up the camera. When using the exposure meter, you also need to set the photosensitive speed of the film or CCD. In addition, in the absence of exposure (photometry) instrument, the empirical exposure meter on the film box or in the book can be used as a reference for shooting conditions.