Thank you very much! Yes I have just seen those signs in the book.

I would love to have also the "=" sign, i.e., chips sold at the same price as the previous year. Here, in the book, when there is no sign, I suppose it just means that the value of the chips is the same than the previous year, but it does not mention if this chip has been traded or not. Do you confirm this?

When you have "+", or "-", you know for sure that the chip has been traded.