In addition to what others have noted it would be worth knowing what you are trying to find out. If you are trying to find out how long it will take to download something then the only valid test is to download it. There is after all no point knowing how long it will take you to drive to Edinburgh if you, in fact, want to go to Liverpool.
If you want to know the fastest speed your line can handle then that could be tricky. The only valid test there would probably be to use a tester based at your telephone exchange. Or maybe even one based in your cabinet (for FTTC) or aggregation node (FTTP). But in all those cases the result wouldn't be all that helpful either because that's like knowing how quickly you can get out of your housing estate.
The best use of speed testers is to run them fairly frequently and learn to know what they typically report. That way you can spot faults if they don't report what they normally do. The Thinkbroadband tester is particularly good because it reports both single threaded and multi-threaded with graphs.
Of course even then the tester on its own doesn't tell you where the fault is but at least you can post the result somewhere on here (preferably your ISP's section) and if other people say they see the same thing you can perhaps rule out your equipment being the cause and use the responses as evidence when talking to support.
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Andrue Cope
Brackley, UK
Edited by Andrue (Sat 01-Feb-25 21:14:26)