What has the DM41 extra over the HP42s?

[hth]

I can add that the HP-41 and HP-42 were made with different goals. The HP-41 was an extensible system which makes it more than a calculator. It was actually a base model, but eventually no more advanced model were created thanks to the way it could be added to and configured by the user. The HP-42 is a calculator much like the HP-15C, but also based on the ideas from the HP-41. It was made later and should be more refined, as they could base it on more previous experience. However, not everything carried over and some people just prefer the older model thanks to the way it was more than a calculator. If you do not really know what you want, or if you just want a calculator and are happy with user programs, then you will probably prefer the HP-42. If you have experienced the HP-41, like to explore things and tinker with it at a much greater depth, then you will probably want the HP-41. Another aspect is the huge existing software base for the HP-41 which you may like to explore.