This app can derive ambient temperature readouts on devices which otherwise lack dedicated ambient temperature sensor¹. This is called the derived temperature sensor. It doesn't use the Internet, but computes the ambient temperature based on other sensors inside the device. Accuracy of the method will vary from device to device, but it should generally stay in the range of ±1°C up to ±5°C (maybe more if your device is not cooperating well).
Temperature data can be put to good use by the barometer, to further improve on (already great) barometric altitude accuracy. This option is called a Thermo Barometer, and can be found in Settings→Tracking→Altitudes, or the Control Panel. It is turned off by default. Please turn it ON only when the device is exposed to the open atmosphere, eg. while walking, running, biking, paragliding, or similar! Otherwise you can get errorneous altitudes and other related readouts.
There is an option in Settings→Advanced→Temperature where you can change the type of the derived sensor and influence the calculations. Currently there are two types: Type A and B. Type A should work well on majority of modern devices, including premium devices like Samsung Galaxy, Sony Xperia and other ultra-slim devices, and devices with big screens like tablets and phablets. However, some devices are simply built differently so there's also the Type B, made for somewhat more bulkier and/or compact devices like Sony Xperia Compact series, and devices like some Motorolas or HTCs, just to name a few. If you feel the calculations of one sensor type are incorrect for you, simply try the other type.
Note! Please turn the Thermo Barometer option ON only when the device is exposed to the open atmosphere, eg. while walking, running, biking, paragliding, or similar! Please keep it OFF while in pressurized, closed or air-conditioned vehicles like cars or airplanes! Otherwise you can get errorneous altitudes and other related readouts.
Note! This sensor may need several minutes to settle down on temperature change, due to physical restrictions of the method. Also, if the battery of your device is not genuine, is of poor quality, damaged, or if the device is connected to a charger, please expect more inaccurate readouts. Temperature readouts will also generally be higher if you are holding the device in your hand, because your hand is heating the device.
¹ Vast majority of devices today don't have a dedicated ambient temperature sensor