Hi apmuthu, your prompt reply is highly appreciated.

As I mentioned in the beginning that I am a new user and it just might be my lacking in understanding!

I understand that the fresh purchase rate has to be manually assessed and when I do that the automatic cost update takes the average of the old rate and the new rate and which is absolutely right.
But when I call for a report of inventory valuation of a past date prior to this fresh Purchase with new cost rate, it shows the new average rate of that particular inventory item which changes the value of that particular item, when the fresh purchase is yet to occur in a future date!

Shouldn't the new average rate be effective from and/or after the fresh purchase took place and Not before?

I am a new user from Bangladesh.
There are opening Balance of Inventory with a specific rate with accordance to the value in Balance sheet, say as of July 01, 2015. When I purchase a certain quantity of the same item today with a different rate, an automatic cost update takes place calculate an average cost which should be fine for today onward.
But the problem is, when I check my inventory valuation as of July 01, 2015, the rate is changed to cause the value to be different even though the quantity remained the same as it was.