Data Validation Lists - Creating lists based on data from another list

Hi there,

Im trying to make reporting processes easier by being able to select operational centres within a business unit. I need to be able to set up both as data validation lists (drop down lists) but need for the data to change based on selection from the first data validation list.

For example, when you select BIF as the business unit, i only want a list of operational centres under them to be in the data validation list. When you select PAE as the business unit, i only want there operational centres displayed.

I have tried a few ways to do this - but am totally lost.

I have attached a sample spreadsheet detailing what i mean.

Any help that can be provided will be greatly appreciated.