For my dissertation I am preparing a list of symbols used in the text, which basically is a table that consists of the symbol, a short explanation and the dimension it has as indicated below:
Symbol Description unit x way travelled by the thing km z fraction of the x and the total possible way ?
My problem lies in the second symbol "z" which is a dimensionless quantity. I could of course just leave the unit column empty for such quantities, however that would look a bit like there was something forgotten and therefore I would like to indicate somehow that this symbol denotes a dimensionless quantity. Is there a convention to indicate that a unit is dimensionless?