I drive a Toyota Asian Utility Wagon powered by a 2C 2000cc Diesel engine since July of 2012.

I used to drive a 33 year old petrol engine 1979 Toyota Corona station wagon and fuel wise was uneconomical, then I became conscious with my kilometers to liters ratio so I reviewed and took notes everytime I refilled my tank.
Since July of 2012 I have been using Shell Diesel fuels and regularly filled up 22 liters at the start of the week as my budget 
Since August of this year I decided to switch to Petron Diesel Turbo, they claimed it has higher Cetane rating than all of the other diesels in the market. Review found here --> http://www.gadgetsmagazine.com.ph/uncategorized/cetane-boosters-optimize-performance-of-petron-turbo-diesel.html
Indeed! The difference in performance was immediately noticeable. Engine idle is smoother, engine operation is more quiet and increase in acceleration was very noticeable as well as the top end speed.
My Km reading has increased too, I averaged 170km with 22L with Shell Diesel fuel and now averaged 180km with the same quantity of 22L with the same daily routine, same driving conditions
and so my 22L lasted a day or two longer 
How is Diesel Cetane rated?
What are the standard Cetane ratings for diesel and why can't petrol stations post the Cetane rating like how they post the Octane rating for their gasolines.
Thank you 