Program Shift is indicated by the letter P setting on a digital camera. In this mode the camera automatically selects the shutter speed and aperture for an appropriate exposure. Afterwards, however, you can simultaneously change the shutter Speed and Aperture settings while maintaining the exposure. So, even if the shutter speed and aperture values are changed, the picture brightness remains the same.
For example, a 1/80 of a second shutter speed and an aperture number of F8 will result in the same exposure as a 1/200 of a second shutter speed and an F5.6 aperture number.
NOTE: Not all cameras have a Program Shift option.To know if your camera has the Program Shift option, check the specification or supplied operations guide.