HP-48S vs. 48G vs. 42S

[Ron Ross]

Sylvain Cote has excellent advice. However, if you cannot wait for September for a replacement, I suggest you buy an Hp 50G or an Hp 48G+. Both are RPL calculators and based upon the Hp 28s and aside from the keyboard, very similar to your Hp 28s. AND both can save and load programs onto a PC so that any programming you do will not be lost with a battery change!
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The Hp 50G has a modern USB interface and an even more popular SD card interface (limited to 2 GB max). The Hp 48G series needs an RS-232 interface and probably older OS on PC to actually upload or download programs. By the way, hpcalc.org is an excellent repository for programs for ALL Hp RPL calculators.
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I suggest the Hp 48G series, probably the G+ as it might become your favorite calculator (it may not, as you may like the fold out Hp 28s forever). As for your Hp 28s, I suggest you buy another as well. They aren't making more. However, I may also suggest you consider an Hp 28c as their battery covers seem to have less breakage problems. Downside is miserably small amount of RAM, but you will be using your new Hp 48G+ or Hp 50G for all of your new programing anyway!!! 8^)