Excel::Writer::XLSX uses the same interface as the Spreadsheet::WriteExcel module which produces an Excel file in binary XLS format. A forecast sheet created by Excel contains two columns with your original data (timeline series and the corresponding data series) and three calculated columns (forecast values and two confidence bounds). My formula is '=FORECAST.LINEAR(I2,$C2:$H2,$C1:$H1)' FORECAST - predicts future values by using linear regression a legacy function for backwards compatibility with Excel 2013 and earlier. You can do such a forecast with your own formulas or have Excel create a forecast sheet for you automatically.
