Help with comobox linked to previous combobox (dependancy) on a userform

Hi everyone,

I am working on a summary report that starts by asking the user to provide it with a few key components with regards to the unit that was tested.

There are two sections: info with regards to the unit that was tested and the second pertains to the results. I am having trouble with the first section. Upon opening the userform (HistoryInfo) the user should be able to select a unit operation from a dropdown list (combobox is linked to a named ranged "UnitOperation"). Until this point I am able to get the userform/combobox to work as I wish, it is the next section that I am having trouble with.

Then the second dropdown should list the sizes that is available in the option that was selected in the first combobox. This should also be drawn from named ranges. The idea is that the comboboxes should have the same functionality as the INDIRECT() function, but it has to be on a userform. In a similar scenario, the advice was given to use a combobox along with a list box, but I dislike the idea since the list of available sizes differ. Any advice on how to get this to work will be much appreciated

I have attached the summary file to show what I currently have and where it is that I need help. The userform is on the Information sheet and the named ranges is on the Names sheet.

Please, help?

TL33