Set form default value to most recent field of certain combination

[howToMSAccess]

Hi, in my AssemblyParts table, I have fields, "Part A Serial #", "Part B Serial #", "Date Tested", and "Other Info".

For my form, I have the entries: "Part A Serial #:" "Part B Serial #:" "Date Tested:" "Other Info:"

I'm having trouble setting "Date Tested" to autofill to the most recent "Date Tested" of the specific serial # combination I enter in my form, corresponding to the data I have in my AssemblyParts table. Any help would be appreciated.

EDIT:
As for data: my table is called "CalibrationData". Within it, I have fields, "partAserialNumber", "partBserialNumber", "DateTested", and "ImpactForce". For this table, there are numerous combinations of partA and partB, and Impact Force calculations could be made multiple times a week for the same combination of partA and partB. Thus, in my bounded form, what I envision is that as I enter in partA's serial number, and partB's serial number, "Date Tested" will autofill to the combination's most recent date stored in the "CalibrationData" table

[jforbes]

You could use a DMax for this. Create a Unbounded field and set the ControlSource to something like this:

=DMax("DateTested", "CalibrationData", "partAserialNumber='" & [partAserialNumber] & "' AND partBserialNumber='" & [partBserialNumber] & "'")

You may need to add a Recalc in the OnCurrent event for DateTested field, as well as the OnChange event of the SerialNumber fields.