Thanks kettan. I tried the first method, and it works. But i got another question: if i want to add +/- for percentage changes as well, and i can't have text, what should i do? Custom format can add +/- but then it must have fixed decimal numbers. Thanks
I've set up another option in the attached, instead of using a string in the option 2 worksheet there are two separate measures, each of which is set up to return Null or the value. You can then use whatever custom formatting you want on each. the cells are centered using the Text Shelf formatting, the header is aligned using header formatting.
Also, an alternative (or addition) to doing the +/- would be to use color, either in a highlight table or by coloring the text directly.