CPI April 2015 and DA & Date of effect. 

Consumer Price Index Numbers for Industrial Workers - CPI(IW) for April 2015 is 256 points, increased by 2 pointscompared to March 2015.   DA as on April  2015 is 117.69% Likely DA as on July 2015 is likely to be 118 % or 119%.

This shows once again retail prices are going up even though the inflation level is at negative figure. The vast difference is there between whole sale prices and retail prices.   

Now it is clear that the wages should be calculated taking into the prices as on 1/1/2015, we cannot estimate in real sense the prices as on 1/1/2016.  The prices may increase or stabilize which depends upon rainfall, crop supply, demand supply etc. 

technically it is incorrect to project the percentage of price rise as on 1/1/2016. Hence the date of effect of 7^th CPC should be only 1/1/2015 not 1/1/2016.

Source:www.karnatakacoc.blogspot.in