When using the powerful Refinery Calc engine a user can select to run the refinery by fixing the crude diet percentages or select “optimized” mode in which, the RC Engine will optimize (choose between) light and/or heavy crudes. In optimize mode, the First Crude Selection is setup for a “light Crude Slate”, the second, third and fourth selections are setup for intermediate crude slate selections, which are fixed and the 5th crude slate selection is reserved for a “heavy” crude. The RC Engine will then optimize amongst the crude slate selections and solve to objective functions: 1.) Max Margin and 2.) Max Crude Throughput. In fixed mode, the RC Engine optimizes the refinery per the criteria above, but does not take into consideration optimization between the light and heavy crude selections (because they are “Fixed” by the user).