That will depend on your definition of "previous". The GetNthRecord function to copy data from the record immediately preceding the new record in your found set in an auto-enter calculation.
But sometimes that's not the "previous record" that you want and then you have get creative with other means to find and access that previous record via self join relaitonship, ExecuteSQL query or a script performed to both create the record and copy over the needed data.
It's also possible to set up a running total summary field to make such a computation.
is there any way to make a button for lack of a better term that will force the record to "re-get" the information from the previous record?
example: record 1 starts at 100, subtracts 20, subtracts 10 (all in separate fields) with a total of 70. new record gets it start information from previous record - 70, then subtracts 20 and subtracts 20 to end with 30. So lets say in record 1 i made a mistake and I needed to subtract 25 and 15 instead. I would go to record 1 and change 20 to 25 and 10 to 15 and my total would auto change to 60, but the next record wouldn't change with it, so here's where I want the "re-get" info
hope that makes sense, I'm not strong with the filemaker lingo
A script can certainly use getNthRecord or a self join relationship to update a field with data from the "previous" record.
but maybe you don't have to.
Consider the Bookkeeping Ledger example found here that keeps a running total with values added or subtracted from the running total in each record: https://dl.dropboxusercontent.com/u/78737945/AccountingLedger.fmp12
when used getNth, things were going fine, until i started deleting some records now i just get the ? error when I create a new record. i tried changing the next value for a 'fresh start' and still no luck
I suggest that you look at the example file that I posted which does not use getNthRecord. There is a limit to the number of times that one record can link to another as this sets up a recursive chain of calculations. This limit is reached much more quickly in FileMaker Go than in FileMaker Pro, but this limit still exists in FileMaker.