A formula works in the first row but produces incorrect results after being copied downward. Often the arithmetic is fine; a reference has moved when it should have stayed fixed. Cell references tell a formula where to obtain its inputs. When copying, you can allow the column and row to adjust or hold either one in place. A small order list is enough to demonstrate the difference.
A reference that follows the next row
Suppose column B contains unit price, column C quantity, and column D total price. Row 2 contains 12 and 3. The formula =B2*C2 in D2 returns 36. Copy it down one row and it becomes =B3*C3. That is desirable because the next order should use its own values.
B2 and C2 are relative references. For copying purposes, they describe a relationship to the formula's position. Moving one row down changes the row number; copying one column right changes the column reference accordingly. References in the same formula do not all need identical behavior when they represent different kinds of input.
Do not judge a copied formula solely by its result. If two rows happen to have the same price, an incorrect reference may initially return a plausible amount. Inspect the formula in the second row and another farther down, checking which cells they actually use.
Keep a shared assumption fixed
Now suppose every order uses a discount entered in F1. Enter 10% there, for example. The formula =B2*C2*(1-$F$1) still uses price and quantity from the appropriate row but keeps pointing to F1 when copied. In this example, the result is 32.4.
The dollar sign before F fixes the column; the dollar sign before 1 fixes the row. Together, $F$1 remains the same reference when copied. Without those signs, copying downward would change F1 to F2, F3, and so on. Empty cells or unrelated values could then produce unexpected results.
A fixed reference does not protect the input cell or its value from editing. If the discount in F1 changes, dependent calculations are meant to respond. Label that cell clearly and state whether it contains a percentage, amount, or another quantity. Calling it merely a factor would be unnecessarily vague.
Fix only one direction
For a small comparison matrix, place quantities in A2, A3, and subsequent rows, with different unit prices in B1, C1, and subsequent columns. In B2, use =$A2*B$1. It always obtains quantity from column A and price from row 1.
Copying it to C3 produces =$A3*C$1. Each component may move in one direction while remaining fixed in the other. Mixed references are useful when a formula is copied both downward and across. Do not add dollar signs everywhere as a precaution; that would prevent the adjustments you actually want.
Verify with simple numbers
Begin with a few cells whose results you can calculate mentally. Change exactly one input and observe which results respond. If an expected result stays unchanged or an unrelated row changes, inspect the references.
These examples describe copying formulas. Moving cells, inserting rows, or renaming sheets can cause applications to adjust references under different rules. Inspect formulas again after structural changes. Correctly placed dollar signs do not remove the need to review a workbook that has subsequently been reorganized.