There's no redundancy. Imagine you have 2 buckets, you reach into bucket A and grab some cash and put it in bucket B. $x dollars leaving bucket A is entry part 1, $x dollars entering bucket B is entry part 2. That's all it is. I honestly don't understand what single entry is by comparison - it sounds like losing an essential attribute of the transaction.
A creative hobby in which you could apply your programming skills perhaps?