I am trying to build a validation rule that will require a date when 1 of 3 fields are updated.  Initially I did

AND(
Asset_Update_Date__c = PRIORVALUE(Asset_Update_Date__c),
OR(
ISCHANGED( Unmanaged_Muni_Assets__c ),
ISCHANGED( A_Share_Assets__c ),
ISCHANGED( C_Share_Assets__c  )))

That only works if a date is already in the field. 

These fields will initially start off blank as will the date.  What I would like to see happen is when a user updates any of the fields that it requires the Asset_Update_Date field to be updated to the current date.

Thanks

I am trying to build a validation rule that will require a date when 1 of 3 fields are updated.  Initially I did

AND(
Asset_Update_Date__c = PRIORVALUE(Asset_Update_Date__c),
OR(
ISCHANGED( Unmanaged_Muni_Assets__c ),
ISCHANGED( A_Share_Assets__c ),
ISCHANGED( C_Share_Assets__c  )))

That only works if a date is already in the field. 

These fields will initially start off blank as will the date.  What I would like to see happen is when a user updates any of the fields that it requires the Asset_Update_Date field to be updated to the current date.

Thanks