50g

http://h20331.www2.hp.com/hpsub/cache/383680-0-0-225-121.html

Some simple training guides which are a good starting point.

> Are there any good books or PDF files available that have more info
> than the "User's Guide"? 
> Something like a reference manual and
> something that tells how to do things like check your ROM version. 
> Also maybe a good programming guide.

http://h20000.www2.hp.com/bizsupport/TechSupport/DocumentIndex.jsp?contentType=SupportManual&lang=en&cc=us&docIndexId=179111&taskId=101&prodTypeId=215348&prodSeriesId=3235173

In just that alone you have ~2000 pages of documentation.  In the AUR,
you have everything from a complete table of all commands and basic
programming, to how to do ARM assembly on the calculator.

TW