Just starting out with Tableau. The application creates metric that are simple values, such as average, median etc. for the scope defined by the dimensions on the pills, i.e., if the pills are region, product and date, and Sales is the measure, we can see the average cost, total cost etc. base don what we select in right click-drop down box. What I want is to show the weighted average cost, where the weight is based on price for the products within the region, product and date combination. I am not able to understand how to distinguish between a calculated field in which the calculation applies to individual row of the underlying data or operates on the aggregates (i.e., the variables used on for the region, product and date combination. Also I cannot find anywhere a clear explanation of window_sum etc. What exactly is a window? I read some documents in the website and bought a couple of books, but nowhere can I find a simple explanation of how calculations are done at the row level (record level) and at the particular group level. Would appreciate any and all help to understand this basic issue.