Contactless bank cards

[Peter Tomlinson]

Roland Perry wrote:
> In article <B33B3C603B7644689B64664F1D049B3E at your41b8d18ede>, Tom 
> Thomson or was it Michael? <colinthomson1 at o2.co.uk> 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.
Not all bus ticket machines are the same. I'm fairly certain that the 
Nottingham bus machines will soon be replaced.

Peter