Thanks for your answer Greg,it works.
But only, if there is no other stuff like primes (') present.
The usual way to denote for RMS-values of a quantitiy would be
(\ab(T'\-(m)\+(2)))\+(1/2)
so that the overbar covers the "T", the prime and the square. This doesn't work because the overbar is at the same height as the prime and the square.
Do you have any solution?
Ralf Kapulla