Roland Perry writes:

In message , at 13:24:29 on Tue, 28 Feb
2012, Adam H. Kerman remarked:
Is the terminal the waiter brings to your table exchanging telemetry
wirelessly during the transaction, or does it have to be plugged into
a base station elsewhere in the restaurant? I assume it's wireless.

They are connected wirelessly (to a base within the retailer's
premises), Bluetooth apparently:

http://www.paymentsense.co.uk/card-processing/perfect-
terminal/portable-terminals/

Are they robust enough to be used where fare collection with a hand-
held device is warranted, if gawd forbid we talk about transport, or
would a more robust hand-held device be used on trains?

Outwardly similar devices are available (they don't use regular retail
handhelds communicating with a base station on the train):

http://en.wikipedia.org/wiki/Avantix_Mobile
On the trains here in rural Shropshire, the ticket collectors carry these, with a chip and
pin reader attached.