Why Consumer Price Index is more Accurate in Monitoring Our Investment Against the Real Value

A sample of how CPI and Inflation are computed (Click to Blow Up)

I realised that monitoring CPI from the day we started investing is much more accurate and useful than averaging inflation rate. Say for instance, if I started investing last 2006 up to until June 2014 and if I simply average the inflation starting from that year to June 2014, I could probably get more or less 8% only. But, if I based it from CPI last 2006 to June 2014 and calculate the rate of change, the result would be 39.6% which means my total capital investment since that year lost its value by 39.6%.