The farmer uses the 40 Kg stone on a balance scale to weigh out 40 kg of feed hay bales. His buddy down the lane asks to borrow the balance stone for a while. He says sure. The buddy comes back a few days later, says 'sorry, I broke the stone accidentally into 4 pieces'. He comes back to apologize again a few days later and says sorry again. The farmer says, its ok, the four pieces you broke it into allows me to weigh anything from 1 kg to 40 kg just using the stones and the balance.
What is the weight of each broken piece that allows the farmer to weigh anything in 1 kg increments from 1 to 40 kg just using the pieces and the balance?