# Back Calc Input Dialog

The 'Back Calc Input' functionality is used to attempt to determine an input value for a specific element's property that would achieve a desired result in another element. This dialog allows you to run a calculation, changing the value of a single property for one element in each iteration, and saving the accumulated results to a spreadsheet, highlighting the input/result combination that most closely matches your required value. Additionally, you can view the progress of the calculation in a chart. To display the Back Calc Input Dialog: ▪Select the Tools | Back Calc Input menu item. Toolbar Buttons •Use the toolbar buttons to open an existing FBC (FluidFlow Back Calc) file; save the values you're working on to a file; and refresh/update the Element and Property drop-downs based on the currently open flowsheet. •The 'Run' button will execute the "back calc", and on completion update the Closest Match match field, generate a report, and refresh the chart. (Note: Some models may take some time to complete if there are a large number of steps/runs to perform.) How it Works Select your "Target" and "Source" values. The Target is the element and (result) property that you want the "back calc" process to achieve. The Source is the element and (input) property that you'll change to try to achieve the target.
Field | Description
Target | Element | Select the Node/Pipe which you want to evaluate a property value for. When you select an element, the Result Property drop-down is updated to reflect the available properties for that particular element.
Target | Result Property | Select the property that you want to test for. When you select from the drop-down, the Value "units" field is updated to reflect the currently selected result units for that property (if applicable).
Target | Value | Enter the Value you want to achieve. This will be in the result units applicable to the "Result Property" you've selected.
Source | Element | Select the Node/Pipe which you want to base the "back calculation" on.
Source | Input Property | Select the Input Editor property for the Element that you want to change.
Source | Start/End/Change | Enter the value to start with, the value to end with, and the increment/decrement change you want to change the value by in each iteration. When you run the back calc, it will initialise the input property to the Start value, increment/decrement by the Change value, and calculate until the End value is reached.
Closest Match | This is the value the Input Property should be set to to come nearest to matching the required Result Property value of the Target Element.
Report Results This records the input and result values for each calculation in the 'Back Calc'. The Closest Match - the input property value and the calculated result property value - is highlighted in red. Use the toolbar buttons to save the report results to an XLSX file, or to preview it (for printing) in a spreadsheet. Chart Results This is a visual representation of the Report spreadsheet. Use the toolbar buttons to save the chart to a JSON-format file; to insert the chart into the current flowsheet as a Chart Object; and to toggle the "Closest Match" data label.