The sky speedtest measures the speed from sky, to the sky router.
Fast.com measures the speed from Fast.com to the device requesting the speedtest.
In most poor speedtest results reported here, users were using old 2.4G mobile phones which simply dont have the capacity and reliability to carry out speedtests.
Speedtest need to be carried out by using a gigabit ethernet cable and laptop/computer with a gigabit lan to give accurate speedtest results.
