Ending [Krugman] here. First start with your definition of 'inflation'. In my perspective, that would be the increase of the money supply (in the broad sense).
And how would you measure it?
I guess I am condemned to believe the official data from Central Banks.
Yes, but they're not providing data about inflation by your definition. They're just measuring price changes of various goods. I was asking, how would you measure increase of the money supply.
exactly as you say, measuring various price changes in goods. Imagine you have measure the water level in a huge lake then you would take measures on various scales previously set-up. Hope this explanation helps