In traditional spreadsheets, the semantic value of the numbers is lost. The number in cell B2 is not "the number of cars sold in the month of January", but simply "the value in cell B2". The formula for calculating the average is based on the manipulation of the cells, in the form codice_1. As the spreadsheet is unaware of the user's desire for D to be an output column, the user copies that formula into all of the cells in D. However, as the formula refers to data on different rows, it must be modified as it is copied into the cells in D, changing it to refer to the correct row. For instance, the formula in D4 would read codice_2. Excel automates this later task by using a relative referencing system that works as long as the cells retain their location relative to the formula. However, this system requires Excel to track any changes to the layout of the sheet and adjust the formulas, a process that is far from foolproof.