Sola calculates your daily UV dose based on many variables.
At the core of the mathematical equation is the so-called Minimum Erythemal Dose – MED – the shortest exposure to UV radiation that causes the reddening of the skin within the first few hours of exposure that goes away after 24 hours.
Because UV radiation varies over time, the calculation takes that into account by integrating the area under the curve between the start time and the end time as highlighted in the UV chart. It is directly proportional to UV index (the higher the index, the higher the dose) and inversely related to skin type, present tan, sunscreen SPF, and whether flips are involved or not.
There may be other factors affecting the precise amount of UV exposure, such as cloud cover, water proximity, particular health conditions of your skin, specific medication you may be taking, lotions you may be using, your age, and so on, therefore the computed UV dose is only to be used as a general guidance and not as a precise measure.
Daily UV dose is the addition of any “earlier” UV exposure you may have gotten during the day, as well as “current” UV exposure you receive from your current sunbathing session.
If you forgot to use the Timer for a previous sunbathing session earlier in the day, you can use the Start and End time pickers along with other options to save the session so that Sola can take it into account for computing your current UV dose.