The service measures the bandwidth (speed) and latency of a visitor's Internet connection against one of 4,759 geographically dispersed servers (as of August 2016) located around the world. Each test measures the data rate for the download direction, i.e. from the server to the user computer, and the upload data rate, i.e. from the user's computer to the server. The tests are performed within the user's web browser or within apps.