Contactless bank cards

Roland Perry lists at
Thu Nov 18 08:08:53 GMT 2010

In article <B33B3C603B7644689B64664F1D049B3E at your41b8d18ede>, Tom 
Thomson or was it Michael? <colinthomson1 at> writes
>> I've never actually found a machine to try my card out upon. But the
>> Oyster pads in London require the card to be pretty much out of a wallet
>> and touching the surface. Similarly the RFID cards used on the buses in
>> Nottingham. The technology is dozens of order of magnitude away from
>> scanning the bus pass in the passenger's pocket as he gets on board.
>> --
>> Roland Perry
>Well Roland, I usually understand "orders of magnitude" as decimal 
>ones,  But even if I were to assume that you meant binary orders of 
>magnitude (which would usually suggest to me an intention to mislead, 
>but let us assume that although you meant binary you had no such 
>intention) "dozens" means a factor of at least 2 to the 24th, or 
>something a bit bigger that 2 times 10 to the 7. If I guess that 
>there's an inverse square law in there somewhere,

Apparently it's an inverse 4th power, and the Nottingham bus passes have 
to be held pretty much *on* the reader[1] - no more than a millimetre of 
air gap is acceptable.

[1] Which is quite tiresome when you have several senior citizens 
boarding, who seem to find the technology difficult, and it takes a 
while for them to position their cards exactly right.
Roland Perry

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