Well first of all insert the Duration1 column. To do this, right click
on one of the headers on the left hand pane of the Gantt chart and
Then right click on the Duration1 column header and click Customise
Try the following two formulas:
ProjDurConv( [Duration] , pjDays )
ProjDurConv( [Duration] , pjMonths )
You will see that they display respectively the duration in days and months.
So now you have to do the conditional element.
In a manner similar to above, insert the Flag1 field. Against each task
in the plan, set the value to be True if you want the duration displayed
in days and false otherwise (the values are set from the drop down boxes
as you click on each cell.
Now insert the following formula for the Duration1 column:
Iif( [Flag1] = True , ProjDurConv( [Duration] , pjDays ) , ProjDurConv(
[Duration] , pjMonths )