You have many options when it comes to buying a HP 41 on ebay. Be sure that you are choosing the right one for you. Here I offer some safe buying tips and a quick guide to some of the more common versions available online today.

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Warnings:

Always watch out for battery corrosion and broken internal posts!! 

Ask the seller before you buy and if they do not have pictures of the battery contacts and can't tell you if the case is firmly held shut, assume the worst.

Special Models and Screen Appearance:

Blanknut- Keys are not labeled to allow customization. Alpha/HP labels are not present on bottom or rear of calculator. Hard to find!
Fullnut- Screen corners are square - 90 degrees and sharp
Halfnut- Screen corners are curved (e.g. rounded or bezel)

picture 1: A 41C Fullnut Blanknut            picture 2: 41CV Halfnut       Picture 3: NEW Halfnut 41CVs    

ROM versions: The latest ROM versions are:

• HP41C -  HFF
• HP41CV- HFF
• HP41CX- NFL

Room for Expansion:

• HP41CV is equivalent to a HP41C with 4 each 82106A Memory Chips or a QUAD Memory module
• HP41CX is equivalent to a HP41CV with Extended Functions, and TIME module