Their previous app collected a lot of information on mobile phone coverage around the world using information about battery temperature. The logical next step was to invent the calculation to make an average of battery temperatures and make these readings of ambient temperature. The calculation works when it's averaged over an area of a large crowd of users. It has to be part of the bigger process. Samuel Johnston at OpenSignal explains, It is helping to show what the weather id like for everybody. So it we have 100 users for London, we can collect the correct temperature for London. It's a way to calculate an average, so for each individual phone it may not be correct.