This is the second strange thing I found:
for a calculated field, when trying to write the formula, I can use *, + but I don't have the option to use -, / . Those keys won't work...
So, I'm trying to write F8-F6, and I can't write the minus sign.
Also, I don't seem to have the option of using a number, let's say F8*0.09, which would be useful for tax calculation, etc...