New HP 28S, strange behaviour

[Jlouis]

Your HP28s looks normal,

the numbers you mention is the stack numbers.

Maybe you are used to algebraic calculator and does not know RPN.

HP 28s is a calculator with RPN entry logic.

Please refer to this page of this site to learn RPN:

http://www.hpmuseum.org/rpn.htm#learn

Theres also a good youtube video that explain RPN very well:

https://www.youtube.com/watch?v=cPKg_JtI-Ys

Don't forget to read the calculator manual, where it explains how your calculator works.

If you don't have it, you can order a scanned pdf one here in this site.

After you did all of these, if you have others doubts, please ask here.

Hope I have helped

Cheers