My time was that of the ...HP-41, *the* engineer's favourite, with input/output ports and superb I/O capabilities (the famous HP-IL loop), and too many extensions to mention. Favourite, that is, until the HP-48 came along; but it's a different beast, from the 1990's, two "generations" up (if you count the HP-28C/S), with a graphic screen of 64 x 131 pixels, symbolic maths, and RPL programming. It's solid too, has a good tactile and positive keyboard (much better than later models, until the HP-50g), and IR communications and printing. The HP-48GX (and HP-48SX, its predecessor in that respect) is extensible in that it can take up to two cards, of applications and/or memory mainly. If you're an HP fan, then you probably have one, or are on the way to buy one. If you're not, and you're an engineer or scientist, then get one - probably. The calculator is not small, but fits well in the hand. Don't take my word for it (I don't feel worthy!), go visit http://www.hpmuseum.org/hp48s.htm for an introduction and http://www.hpcalc.org for a wealth of information.