security features such as passwords and access limitations to prevent unauthorized access to sensitive casting operation parameters such as the desired pressure recipe stored in the local unit 52 but accessible via the master plc 50 data is exchanged between the master plc 50 and the local unit 52 typically as handshaking input output the data exchanged includes the parameters sensed or measured by the remote units 54 the user will be able to vary some of the process parameters of the local unit 52 within predetermined limits such as fill shot number described hereafter the constant pressure hold time length of constant pressure period b and the pressure exhaust hold time length of exhaust period c the fill shot number is used by the local unit 52 to compensate for the decreasing volume of molten aluminum 22 in the crucible 12 as cast parts are formed when a predetermined volume or charge of molten aluminum 22 is placed in the crucible 12 and casting begins the fill shot number is normally zero as parts are cast the volume of molten aluminum in the crucible 12 drops and relatively more pressurized air must be introduced into the space 26 in the crucible 12 above the molten aluminum 22 to get the constant desired volume of aluminum to flow into the cores 20 accordingly a pressure adjustment is calculated by the local unit 52 such that wherein u201c offset u201d is a constant based upon the cast part volume and the initial volume of molten aluminum in the crucible 12 and fill shot number is nominally equal to the number of parts made with the current charge of aluminum the local unit 52 uses the.