My machine has Win7 Pro SP1 installed on it, as well as IE 11.
When my cable Internet provider sends a technician to me to check the download speed, he connects his laptop directly to my cable modem with an Ethernet cable and tests the download speed on www.speedtest.net. His results are identical with the Internet provider's claims.
Immediately after that he tests the download speed on my desktop (connected in the same way) and receives the same result.
A few minutes after technician leaves, I repeat the test and the download speed drops to half of the previous speed.
Such a situation happened to me several times before, on occasion of visits of other technicians.
I wonder if I can 'inherit' e.g. extra open ports or modem settings from the technician's laptop test for a very short period of time, which could justify my perfect download result in test no. 2 and not in later tests. Please note that the value of the download speed isn't essential in this problem.