Why are readily available productivity data relative, not absolute? I've been trying to do some cursory research on labor productivity. In the process, I've noticed that the readily available data in the US, as accessed through either BLS or FRED (yes, I know it's the same underlying data), is all in terms of year-to-year change, or level relative to a fixed year. Is there any theoretical or technical reason for this? It seems like an absolute level of labor productivity should be well defined: GDP divided by total hours worked. Am I neglecting something that would prevent reliable calculation of an actual dollars-per-hour number? If not, where can I find this figure?
The data you ask for is in the OECD stats website under


  Productivity > Productivity and ULC – Annual, Total Economy > Level of GDP per capita and productivity


This is the graph (in 2010 PPP US dollars):



Aternatively, you can compute it manually:


Select a series of constant GDP of your interest. 
Divide it by number of hours for a group of interest.


You can find both series in the above website. GDP is under 


  National Accounts > Annual National Accounts > Main Aggregates > Gross domestic product 


Hours are under


  Labour > Labour Force Statistics > Hours worked