Garion
Retrieve the list sorted by date descending (so the most recent entry is at the top of the list). Then use List operation Head to get the top object and return the valuation attribute of the object returned by that List operation.
Mike
It seems like you are using an additional attribute that is calculated. But you want to show the latest object in a dataview.
Create a dataview and select "Microflow" as datasource. In this microflow, you can do a retrieve sorted by date descending with the option "first" selected. This will result in getting only the latest valuation (In one single action). Now return it and enjoy it in your dataview.