Even the biggest of companies are not immune to spreadsheet errors. Marks and Spencer in the UK had to change their sales growth from a +1.3% to a -0.4% due to double counting in a spreadsheet.
Double counting is a particularly bad problem in spreadsheets as it is extremely easy to add cells which are hidden or already subtotals. As discussed in our spreadsheet best practice, it is critical you build in an many error checks as possible. It is also highly recommended you make use of a spreadsheet auditing tool.
As per the article it also notes that this is not the first time this has happened.
“… In 2012, shares in SuperGroup fell more than a third in a single day after the clothing retailer was forced into a profit warning because of a mix-up between a plus and a minus sign in its forecasting…”.