[EpiData-list] Query on auto calculation of duration between 2 date fields

I need help in writing the command for the following function.

1 have 2 date fields. the difference between the dates can be less than 30 days also in some cases. How can I auto calculate the difference in days between the 2 dates.

Eg.

v01 11/11/2013

v02 20/11/2013

I want v03 to be automatically calculated as a difference between the 2 above dates.

Many thanks Charulatha

Dr Charulatha Banerjee Regional Advisor ( MCH & N South Asia)

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