UPN is another minimal calculator that does basis conversion. Like anyone else, I was unhappy with the calculator that comes with the Newton, and like nearly everybody else I wrote a calculator for my most immediate needs - which are RPN input and basis conversion.
Also I wanted my calculator to be usable with a keyboard and I wanted proper basis translation of floating point numbers. I don't want a floating point number to be truncated to an integer when I apply a basis conversion. I mean, the hexadecimal representation of 1,25 is 1,4 and not 1.
If you are looking for basis conversion routines written in NewtonScript, the source of this calculator might be of interest to you.
This is actually quite an old project of mine, I just never got around to publish it.
UPN with it's source code is covered by the Gnu Public License.
Please send email if you use UPN.