Calculated Metrics: Retain link when nesting

If a calculated metric is used within another calculated metric, the nested calculated metric does not retain a link to the original.  Instead the nested calculated metrics is a copy of the original.  This means if the original calculated metric is changed the nested calculated metrics is unaffected.

Current behaviour:

• Caculated metrics 'A' is nested in Calculated 'B'
• Calculated metric 'B' actually contains a copy Calculated Metric 'A'
• When the original Calculated Metric 'A' is changed the copy within Calculated metric 'B' is unaffected
• Therefore, when calculated metric 'A' needs updating it is necessary to change the original metric and every copy individually (inefficient)

Please can you consider making nested calculated metrics retain a link to the original to prevent us having to make changes in multiple places?