Scripting numerical values based on preceding record value

[Jarvis]

Is there a way to script a number field to be equal to the value of the preceding record + an increment of 1?

I am not talking about the kind of serial number wherein the creation of a record increments the value by 1.

I want to be able to enter a specific record and change the value of a number field to be equal to the value in the preceding record (plus an increment of 1)

[Ocean West]

GetNthRecord ( fieldName; recordNumber )

Is that what your looking for?