How much money will Welsh taxes raise?
How much tax will be collected in Wales in the years to come?
It's a question that's taken on added significance given the UK government's plans to give the Welsh government control of taxes such as stamp duty land tax and to be able (after a referendum) to vary income tax rates (although not separate bands).
Scotland is ahead of Wales on this journey (Silk was in some ways the son of Calman) and will be given some of these powers from 2015. To prepare for that day, the UK government asked the Office for Budget Responsibility to do a few sums on the revenue devolved taxes could raise in Scotland.
The first Scottish tax forecast was published in April last year - and is now a regular feature of financial statements at Westminster and vital for any government trying to balance the books.
So can we expect a Welsh version? Yes, but not yet appears to be the answer. The UK government announced earlier this month: "The government will formally ask the Office for Budget Responsibility (OBR) to forecast revenues from taxes devolved to the Welsh assembly."
The OBR says it has yet to receive that formal request "but we will of course engage with them on our role in forecasting Welsh taxes as appropriate once they do". So don't expect a Welsh tax forecast to arrive alongside the chancellor's autumn statement next Thursday.
Labour say the UK government needs to get a move on. Shadow Welsh Secretary Owen Smith said: "It's disappointing that neither David Jones nor anyone in the Treasury has had the foresight or sense of urgency to ask the OBR to publish a Welsh taxes forecast in time for this year's Autumn Statement.
"Publishing this document would have made up some of the ground that was lost by the UK Government's delayed response to Silk and it would have showed a clear intent on the Welsh secretary's behalf to legislate for Silk sooner rather than later.
"While Scotland will have their fourth version of the document published next week, Wales now has to wait until next year to see its first. In the meantime, David Jones will continue to make unfunded and irresponsible tax pledges without the full scrutiny that OBR figures would enable."