There is nothing like these RPN (Reverse Polish Notation) calculators from HP. But there seems to be two kinds of people: those who love RPN and those who just find it confusing.

I happen to be in the first category and these are my RPN calculators:

• To the left is my HP-15C, a scientific calculator which I have used continuously since the 80's.  
• To the right is my HP-12C financial calculator that I recently purchased. It is also of 80's vintage. This calculator has been produced continuously from 1981 until today. Very impressive!  
• Below is a Limited Edition HP-15C from the re-release in 2011. It is a gift from my children as they knew about my love of these calculators. The re-release is a result of a campaign from users, but unfortunately it was quickly sold out and is no longer available.

RPN is this entry system where the addition of two numbers involves writing "2, Enter, 3, +" rather than "2, +, 3, =". For such simple calculations the number of key presses is the same as for any other calculator, but for more complex calculations is is very logical and much simpler. RPN means Reverse Polish Notation and is well explained on the Wikipedia page. But what it has to do with Poland is beyond what I have been able to figure out.

Sadly it now seems as if the same thing happens to calculators as to wrist watches - both are replaced by mobile phones and many no longer see any need for them. That's a pity!