Returns the last valid, non-blank value in field.
field - any repeating field or related field, or an expression that returns a reference to a repeating field or related field
Data type returned 
text, number, date, time, timestamp, container
Originated in 
FileMaker Pro 6.0 or earlier
If field specifies a repeating field then it returns the last non-blank repetition. If field specifies a related field, then it returns the last non-blank value in the related set.
Note  The last related value will depend on the way related records are sorted. If the related records are not sorted, then the Last function returns a value based on the creation order of the records.
Last(ParcelBids) returns 1500 if ParcelBids is a number field defined to repeat with ten values and contains the values 2500, 1200, and 1500.
Last(Payments::PaymentDate) returns the payment date in the last matching record in the Payments table.
Last(if(IsEmpty(Company);PersonalPhone;WorkPhone)) returns the last non-empty phone number from the repeating field PersonalPhone when the Company field is empty. If the Company field is not empty, the function returns the last non-empty phone number from the repeating field WorkPhone.
Related topics 
Functions reference (category list)
Functions reference (alphabetical list)
About formulas
About functions
Defining calculation fields
Using operators in formulas