In general, when surface values are disabled, computed item columns receive their source "Units Sold". Fact values from the underlying Table section. However, the specific values from the underlying Table section that the computed item uses depends on the nature of the its calculation.
A calculation or computed item function that expects a single value as input uses the underlying values that correspond to the Pivot computed item column cell to be calculated, aggregated according to the aggregation data function applied to the computed item column.
In the previous example, the "Units Sold * 2" column implicitly requires a single cell value. If it is used in a computed item column with an aggregation data function of Sum, all underlying Table section values corresponding to this Pivot cell are summed and multiplied by 2.
If you review the "Units * 2" value for Los Angeles, you see that it is evaluated by summing the underlying Table occurrences for Los Angeles and multiplying this sum by 2.
The ColMax computed item function operates on a range of data as opposed to a single value.
The Avg computed item function operates on the summed, aggregated values corresponding to a Pivot cell. In the case of Los Angeles, this would be the sum of underlying values for Los Angeles divided by the number of occurrences of these values.
This behavior can be most easily seen from the "ColMax Units Sold" column which shows a value of 500 for each cell. The ColMax function interrogates the range of values in an entire column and returns the maximum value found: 500. This is the maximum cell value in the entire "Units Sold" column in the underlying Table section (compared to 1,100 which is the maximum "Units Sold" value shown in the Pivot display).