Challenge 1: A Calculated "Profit" Field — Solution Walkthrough

Calculated field, named Profit:
  =Sales-Cost

For a product with total Sales of 5000 and total Cost of 3200 across
all its transactions:

  Profit = 5000 - 3200 = 1800

What this figure actually represents:

This 1800 is the TOTAL Sales for that product across every one of its
transactions, minus the TOTAL Cost across every one of its
transactions — computed once, on the already-summarized numbers. It
is NOT the same thing as calculating each individual transaction's own
profit (that transaction's own sale price minus that transaction's own
cost) and then adding all of those individual profits together —
though in this specific case (simple subtraction), both approaches
would happen to arrive at the same final number, since subtraction
distributes cleanly across a sum: total(Sales) - total(Cost) equals
the sum of each row's own (Sales - Cost).

Why the distinction still matters:

The equivalence above only holds because Profit uses simple
subtraction. The moment a calculated field involves DIVISION —
exactly like this chapter's own Profit Margin example, (Sales-Cost)/
Sales — that equivalence breaks down completely: dividing two TOTALS
is mathematically different from averaging many individual per-row
divisions. A calculated field always computes on totals, with no
option to switch to "average of individual row results" instead —
that's a structural limitation of calculated fields, not something a
different formula could work around, per this chapter's own warning
box.