I have a lookup field for equipment when a user is entering a transfer of equipment.  This form first asks if the user is transferring equipment IN versus OUT.  I want to limit the lookup results to contain only items that are IN inventory ( a field on the equipment table called In_Inventory) when the user selects transfer OUT (you cannot transfer what you do not have in inventory) and the opposite when transferring IN (you cannot transfer IN what you already have with a serialize inventory item).  How can I filter the lookup list based on the In_Inventory field on the equipment table base on a drop down on the form where the user selects In or Out?