When you create a calculated metric, there are two types of metrics to choose from: Standard metrics and Total metrics.
Standard metrics: These metrics are the same metrics used in standard Analytics reporting. If a formula consisted of a single standard metric, it displays identical data to its noncalculated metric counterpart. Standard metrics are useful for creating calculated metrics specific to each individual line item. For example, [Orders] / [Visits] takes orders for that specific line item and divides it by the number of visits for that specific line item.
Total metrics: Uses the total for the reporting period in every line item. If a formula consisted of a single total metric, it displays the same total number on every line item. Total metrics are useful for creating calculated metrics that compare against site total data. For example, [Orders] / [Total Visits] shows the proportion of orders against ALL visits to your site, not just the visits to the specific line item.