When you insert a calculation in an object, you will always need to refer to the columns/rows/cells of the data bearing crosstab. Even if it is a chart - remember that you always have a crosstab "behind" the chart.
A calculation will always need a function as well - e.g. sum, avg, count etc.
function(column reference, row reference, measure reference)
sum(d1, 0, m1)
avg(d-1, 0:-11, m2)
allcount(0, all, 0)