The exposure calculator is easy and intuitive. No typing, no configurations. Just drag each slider (exposure value, ISO, shutter speed, aperture) to the desired values. The other sliders move to make good exposure.
For example, if you change EV, ISO and aperture, the shutter speed adjusts accordingly.
The EV slider never moves by itself, until you use the light meter.
The lower left part of the screen shows a camera viewfinder (provided your phone has a camera and you give the permission). Point to the subject and touch the viewfinder to take a picture and estimate the scene EV.
The EXIF data with exposure data for the picture is shown on-screen as well.
The calculator also estimates depth-of-field (DoF). Just dial aperture, focal length and subject distance. DoF is expressed as numbers and graphically. The absolute limits of depth-of-field, as well as the deltas from the focused distance, are displayed. When the far limit goes to infinity, the display shows "hyp" that stands for "hyperfocal distance".
The distance unit can be metric (m) or imperial (ft). Touch and hold for a second the distance unit label at the right of the distance slider (it is either "m" or "ft"). The distance unit changes when you lift the touch. The spot is rather small to avoid unintentional change of the unit.
A. Exposure value is an absolute measurement of light, but suitable for photography. It is also known as LV or EV100. An EV of 15 corresponds to a fully shiny day. The Sun delivers 1.05kW per square meter (only 43% it is visible light), so EV is indirectly related to the power of the lighting source.