Broadband speed testing

I'm about to try to confirm that a friend is not getting the speed expected on their broadband service.
So I just thought I'd check here using 3 different laptops connected in turn to the same ethernet port on the router.
The BT tester and others say I'm getting just over 4Mbps down, but the ThinkBroadband tester always shows 2.4Mbps and sometimes much lower. The XP and W7 machines are consistent, the Vista machine returns slower results. At one point Think Broadband said it was only getting 600kbps.
Is this all normal, or do I have to try to fault find the Vista machine? Everything looks OK in Device Manager etc.
Also, the BT speed tester says not to test again within on hour. Is there a technical reason for this, or is it just to keep the usage down?
--
Bill

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On 10/07/2012 09:22, Bill wrote:

Try another independent test like iPlayers streaming diagnostics page:
http://www.bbc.co.uk/iplayer/diagnostics
That should help identify any Vista related quirks. It would not surprise me if the Vista internet config was screwed up in some way.

The wet weather (flooded cable runs?) and long wires to the exchange mean my broadband raw speed is currently down by a factor of 3 :(
--
Regards,
Martin Brown
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Martin Brown explained on 10/07/2012 :

The actual transfer rates will always be somewhat less than your reported connection speed.
My usual router connects at 18000kbps, my present router connects at 16000kbps - the above test is showing a transfer of 14000kbps.
--
Regards,
Harry (M1BYT) (L)
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On 10/07/2012 10:33, Harry Bloomfield wrote:

A rough rule of thumb is that actual download speed allowing for protocol overheads is roughly 80% of the raw modem sync bitrate.
Your speed is >30x what I am getting today in foul weather.
--
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Martin Brown
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Or putting it another way, 10Mbps raw will give you about 1 MBps data (ie for every 10 raw bits transferred you will get about one byte of data).
--
Jeremy C B Nicoll - my opinions are my own.

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