Symbol with overbar or underline

[Nikolai Huckle]

Hello,

I am trying to use a certain kind of symbol notation for plot labels with gnuplot (see attached .jpeg).
In TeX mode i can of course use the symbols i.e. zeta, chi, pi etc.
but I am not sure how to create the underline/overbar for the symbols.
It is just a minor thing but maybe somebody has encoutered this before or knows of a solution?

Thanks in advance for an answer.

Kind regards,

Nikolai Huckle

symbol.JPG
Description: JPEG image