can you imagine? for a product which is discontinued, second-hand (although sold as 'new') and over a year old!

Having thought about the matter some more, I think I'll go with the 640. Thew screen size is a LOT bigger
(2.7" X 4.5" as opposed to 2.2" X 3.2"), the difference in weight and size is insignificant (for my purposes)
and some of the objections which have been raised (such as it's said that it isn't really a portable) don't hold
water (no pun intended). Both units have an internal battery with about the same hrs. in which they can be used under
battery alone. AND, I have the mini-SD for Canada (because it fits my GPSMap 420) which can be used with
the 640 but not the 478 (which requires a data card for that region). Having said that, I suspect that in a
year or two, Garmin will come out with a new and improved portable chartplotter (although touch screens
seem to be the trend in their recent products and I imagine that the successor will also have one).

Jerry