Text Formatting ⇒ A circle around one or two letters

[PK_TeX]

Hi,

I need to circle one or two letters, and the letters can be either a capital letter (only one in this case), a digit or two digits.

I used

\def\NRU#1{
\tikz\node[circle,draw,inner sep=1pt,outer sep=1pt]{\scriptsize #1};}

\def\NRD#1{
\tikz\node[circle,draw,inner sep=1pt,outer sep=1pt]{\tiny #1};}

And I have in my text

\NRU{S}, \NRU{1}, \NRU{2} \NRD{13}, \NRD{23} and \NRD{24}

Of course, I want the circleds letters be integrated perfectly in the line (without adding spacing).

My solution is quite good, but there is a slight difference between one and two digits.

Is it a solution for centering and reducing the letters in any cases?

Thanks