What are the uses of Auxiliary Carry flag?

The Auxiliary Carry flag of the Intel 8085 is used to store the carry/borrow from the least significant 4 bits of an 8 bit arithmetic operation. This bit (and the Carry flag from the most significant 4 bits) is needed by the Decimal Adjust Accumulator instruction to convert the result of the 8 bit arithmetic operation to correct 2 digit Binary Coded Decimal format.