How to convert a function into a change_event

I currently have a function I have created to populate a field of cells according to the numbers added to 1st,frequency,spread and cost. the function is currently started by a command button. how can I make this more dynamic so that I can use a change event. The problem I can think of is around ensuring that all the columns are populated before trying to process the function.

any help greatly appreciated

James

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  Clik here to view. from_Function_to_Change_event.xlsm‎ (51.8 KB)