Speedtests

I have BT Infinity and recently had my VLINK modem changed because of potential overheating.
Since then I have done speed tests at Think Broadband and speedtest.net
Today at thinkbroadband.com I got a download rewarding of 20.8 Mbps whereas at speedtest.net (which BT uses) I got 37Mbps.
How can these tests vary so much in the space of a minute?

Use a tool like tbbmeter to show the profile of the downloads during the tests.

If the graph is spiky then speedtest.net is more likely to show a higher result due to its sampling. We take a simpler longer term average to the results.

http://www.farina1.com/vary2.jpg shows this

Thanks Andrew. I'm on a Mac so tbbMeter is not going to work for me.

BT does not use speedtest.net.

One of the links is http://speedtester.bt.com which may be confusing you. Speedtest.net uses the Ookla engine, observed in nearly every tester except BT and tbb.

Try the BT one I just linked to.

Ok our flash based tester at
http://www.thinkbroadband.com/speedtest/broadband.html produces a graph at the end and some have said speedtest.net does, but on current one I cannot see it

Roberto,

You are correct and thanks for correcting me.
Speedtest at http://speedtester.bt.com/ gives me 35Mbps and 7.9Mbps