I have been working through the manual. It is a very good effort, I like how it is put together.
I have found something that is either incorrect, or my understanding of how it should work is wrong.
On page 165, regarding deleting and correcting data, it indicates if you key in an incorrect value and have pressed <sigma>+, that all that must be done is press <sigma>- to correct it. That does change the Xn value, but not the value in the X register, it only decrements X by the value of Xn since that is what was on the stack. I believe Last X should be keyed before pressing <sigma>- to ensure the X value is decremented correctly.