In message , at 10:50:46 on Sun, 26 Feb
2012, Stephen Sprunk remarked:
The two-pass scheme is used in other circumstances, such as checking
into a hotel, when they often "reserve" an estimate of the final bill,
ahead of the day you eventually check out.

Hotels are the most obvious example, but restaurants with waitstaff do
the same thing: they will authorize the card for the subtotal (price
plus tax) plus a liberal estimated tip (eg. 20-25%). Either way, the
actual total isn't submitted until the transaction is
posted--potentially several days, not "milliseconds", later.

The "milliseconds" scenario is when I'm buying hardware from a store,
and am standing at the checkout.
--
Roland Perry