ENTER↑ is a misnomer, long live ENTER:

[rprosperi]

(07-06-2014 05:41 PM)Katie Wasserman Wrote:  

(07-06-2014 05:18 PM)hansklav Wrote:  But I read that the HP-18C only used 'System RPL', and I don't know anything about the difference in the behaviour of the ENTER key between 'System RPL' and 'User RPL', so you might be right that the HP-28C was the first with 'Entry RPN'.

That's correct, user RPL was introduced on the 28C. But it's the user ENTER, not system ENTER, that's relevant to your post.

You're both correct, sorta. The 18C came first and it's OS is SysRPL, although this was not accessible to a user for programming, while the 28C was the first machine with user access to RPL for programming.