Advice on Purchasing an HP

[burkhard]

I think your experience on the 28S was somewhat unusual, although keep in mind it 30 years old or close to it, so anything is possible. More likely those 28C/S (like all the clamshells excepting a late production 19BII) might have broken / cracked battery door issues. Many of those sold on eBay already have that problem and even if you get a good one, you need to be careful with that, as it is a fragile point on that calculator. Still the 28S is a nice machine and not super crazy expensive. I have a nearly perfect one which is a joy to use.

Almost every series has *some* weak point, but treated reasonably well, you can buy one that has lasted for decades and will keep doing so. Some of the problems can be repaired easily, some less so.

Still, I'd
1) Figure out what model does what you want and then
2) Learn its weak points (ask here) and things to look for buying one used.

Was the 28S otherwise your "dream machine"? If so, I'd get another (ask for pictures of the battery door and surrounding area on the calculator itself).