Historical cost means the cost of a plant at a price originally paid for it. Replacement cost means the price that would have to be paid currently for acquiring the same plant. For example, if the price of a machine at the time of purchase, say, in 2010 was Rs.15,000 and if the present price is Rs.85,000, the original cost of Rs.15,000 is the historical cost while Rs.85,000 is the replacement cost.