This screen is used to create/view/edit the Duration Formats lookups. These are used to set how a patient's age is presented and allows the format to vary as a function of age. Normally only one is needed and it is used to set the values in the 'Patient Age Format' field on the Administration|Organisations|Practice screen.

The fields are as follows:

Name - the name of the format
Active - uncheck the box to deactivate the format
Formats tab - it's fields are as follows:
Interval - sets the (inclusive) age (in units of Units) below which this format is to be used (ie less than or equal to 3 years in the above example)
Units - can be years, months, days or weeks
Show Years/Months/Weeks/Days - check the boxes to display the years/months/weeks/days

Note that when adding formats, these can be added in any order. The last entry (999 years) provides the setting for the more than 3 years case.  If no 'Patient Age Format' is set for the Practice, then the formats used are as follows:

If the age is greater than that set for the largest defined interval, then the above table is used to define the format.