It indicates when a carry or borrow has been generated out of the least significant four bits of the accumulator register following the execution of an arithmetic instruction.
Since the most significant digit of this sum is non-decimal (E), adding 6016 to it produces a corrected BCD result of 14516.
It indicates when an arithmetic carry or borrow has been generated out of the four least significant bits, or lower nibble.
It is primarily used to support binary-coded decimal (BCD) arithmetic.
Otherwise, if no such carry or borrow occurs, the flag is cleared or "reset" (set to 0).