I don't understand why sometimes I can't choose a graph by period? I can choose a date range but nothing more. I've also had issues with comparing to other periods, even though I have all green checkmarks in what you must have to do comparisions
Graph by and period over period comparisons require that the X-Axis have a date datatype as the chosen column, in addition to other things. You also need to uncheck the box labeled "Hide date on card details".