Explanation
To create a new custom metric on the account product period forecast component, an admin needs to follow these steps:
Create a custom field on the Account Product Period Forecast object, which stores the forecast data for each product and period combination. The data type of the field should be currency, number, decimal, or percentage.
Create a custom field on the Account Product Forecast object, which stores the forecast data for each product. The data type of the field should be the same as the one on the Account Product Period Forecast object.
Map the custom fields on the Account Forecasting page in Setup, by selecting the corresponding dropdown values for Product Period Metrics and Product Metrics. This will make the custom metric available on the Forecast tab of an account, where the user can select it from the metrics dropdown menu. The other options are not correct, as they either involve creating custom fields on the wrong objects, such as Sales Agreement or Account Forecast Adjustment, or they do not map the custom fields in the account forecast setting page, which is required to display the custom metric on the account forecast component. References: Map Custom Fields of Account Product Forecast and Account Product Period Forecast, Configure Forecast Metrics and Formulas