Get Field Value from previous date
I have a simple database to record flow totalizer values for several stations. My table includes the following fields: StationID, Date, and Value. Data is entered into the table for several stations, Sta1, Sta2, Sta3. I would like to add a calculated field to the table called Flow. For a given station, Flow is the last recorded value minus the current value. How can I create a calculation or script to find the last recorded (date) value for the current StationID?
Thanks for your assistance.