Perhaps I should clarify, your measured internet connection speed will be affected by many factors. Removing as many of these slowdowns will result in greater accuracy. Wireless connections or 802.11 a,b,g, n,ac connect at different speeds plus obstacles like floors, walls, ducting, microwaves etc. have an affect. A wired ethernet connection directly to the cable modem will remove nearly all these issues. Rebooting all the constituent devices is also a good idea. There will still be differences between tests, Most test sites will provide a ping time and a latency figure which are other measurements that can be a concern.
Larry