We have a page about RPN: why it is a better way to use a calculator. So far it is embryonic - we need to go much further in the description. We need to have something simple enough to send to one of our friends, and attractive enough so that he gets interested in it.
I wanted to include an applet of an RPN calculator, but I have problems in storing files in this server - since is not mine. So far I have not been able to include a proper Java RPN calculator - yet.
What I have found is a nice site with emulators in several environments/operating systems - one of them as Java.
You will see that is a nice example. You can start practising with it...you'll probably want to hone your skills with it...just in case...
By the way: it is a very good tool for RPN training. Just make sure to open the window as big as you can: on the right side you will see the stack and the registers, and see the effect of what you're doing on the processor.
Of course: no liabilities accepted if the machine is not a perfect replica of HP 15c. I have not tried to program it, and just tried some examples with complex data; but did not do a full review of it.