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I would like to know what is the CAS in the 49G+, because I have the possibility to buy a 48GX or a 49G+.
Is the CAS so important? what difference gives the CAS to a 49G+ from the 48GX?

CAS actually was first introduced with the Hp28 series and the Hp48 series has many extensions from that. However, compared to the Hp49 series the 48 has next to nothing in this area. CAS was first a simple algebraic manipulation tool. The 48 series allows you to expand and collect terms (try it on any 48). On the 49 this has evolved into symbolic solutions for integration and summation series solutions in variable notation (symbolic solutions), just to name a couple.

However, all the CAS developed for the 49 series was originally developed on the 48 and the older versions of this software are free and available for the 48. The CAS is called Erable and the faster and better OS is called Metakernal. Both make a 48 faster and more powerful for CAS and general operations (not all operations are faster) and you will need at least a 128K RAM card to use Metakernal. This can make a 48 into a 49 low end clone. It will cost you the additional price of a 128K card (You need the 128K card, but you may also want to buy a larger card for Port 2 and above also, another additional cost). And you will still lack speed. And the smooth integration of this software. And you will lack RAM (you may be RAM starved, if you don’t buy memory for port 2 and higher), because all this gobbles up the RAM you bought vs the 49G has this RAM available because the OS and CAS are part of the calculator ROM.

But I use a 48 at home without any of these and feel it is a great calculator. I still like it and use it more than my 49 (both flavors), but I may change my mind after my 49G+ comes back from Hp. Missing keystrokes can be extremely expensive when I am crunching numbers (and not help my reputation either). Error of magnitude is fairly straight forward to catch, but an error in addition may make me off by merely 20-30% and unfortunately on the lower end of scale below my safety factors (not good).

But if the new keyboard proves itself, I must say the 49G series is probably the way to go. It is faster and the CAS is a nice tool (though perhaps not really all that neccessary). I am involved in engineering and almost always interested in a numerical answer, not any theoretical solution. CAS is still not a mature feature either. Also, many of my calculations have to be duplicated or available for review and therefore force me to use spreadsheets or Mathcad on a PC. My general work though is easily done with either, and I favor a calculator as it is very light and portable (my laptop is certainly portable as well, but not in the same league).

If you do a lot of high end calculations (matrix, screen manipulation or any large solver application), the speed of the 49G+ is 3-5 times faster (acceptable, to pleasant to use), where often the 48 series is slow (to painfully slow). Number crunching and straight forward vector calculations are fine and actually easier on my 48.

I feel that the overall durability of the 49 is probably a bit better than the 48 due to a lens cover over the LCD (the 48 is bare and exposed).

Both have advantages, the 48 series was designed to be very versatile and it still is!

I would say this, buy both if you can, but if you have to choose, what are your criteria?
Desk calculator with no travel and access to a math package? Hp48

Desk calculator that will double as a math package (and travel) (ie a student) Hp49

Accounting type work or general addition every so often (adding or crunching numbers) I have to say an Hp48, because you cannot count on the 49 to register every key click!!! (even once in a 1000 is too much!!) And I don’t believe Hp has completely resolved this issue, only greatly improved a keyboard problem.

The speed and keyboard layout are much better on the 49 for alpha entry (program development). This is no surprise as the 49 evolved from the 48 by program developers and NOT engineers. (not bad mouthing this, it is just how it is! This often determines how a calculator or anything evolves). This explains why certain keys are moved off of the keyboard and into shifted functions. Many direct key punches on the 48 became shifted functions on the 49 to ease program usage and versatility. They are still there, just buried or obscured by the newer additions and features.

Just a brief review and not a detailed explanation of the CAS. But I would suggest downloading the Hp49G+ manual and reviewing the CAS features and deciding whether they are invaluable or not.

One thing you will give up on the 49 that is on the 48 is the eq lib. I like it! One is available for the 49 via download, but still not quite as nice to use (not built in and therefore needs to be run every time to use).

Hope this information helped (or more likely confused).

Thanks Ron, very interGXGXesting.
I know, I'll take the 48GX