The exposure calculator displays the calculated EV (see Exposure Value (EV)) in the form of
an interactive calculator.
The ISO sensitivity and exposure adjustment values can be set, and
then the Aperture value traded off against the shutter speed.
Whichever one of Shutter or Aperture that was not last adjusted will
respond to changes in the other three settings. If the calculator
reaches the end of a scale in this adjustment, then the highlight
box will turn red.