The ‘Copy Sales Forecast’ screen is identical to the new/amend/view sales forecast screen as described here. The copy functionality specifically relates to the forecast items, rather than the forecast record itself.
To begin copying a forecast, highlight the forecast you wish to copy from the Sales Forecast List and select Copy from the Sales Forecast Menu. Enter the Sales Forecast header record information in the same way as described here.
Note: If the forecast you are copying is customer specific, you do not need to select the same customer, or indeed make the copy customer specific if you do not wish to.
You do not need to keep the overall date range or frequency the same as the original forecast that was being copied. The total forecast quantity will be apportioned out evenly across the periods defined in the header section.
Once you have confirmed the main forecast details, pressing the Confirm button will copy all items from the selected forecast, along with the relevant forecast totals, which will be apportioned evenly over the date range/frequency selected.
Once the items have been copied you can adjust/add to them accordingly.