Display subtotal after each transaction/selected transactions

I'm often putting breaking down my transactions from one bill to each subcategory (at least till the feature with breakdown in the single transaction will be implemented) and would like to see the sub-balance value to verify if I didn't screwed numbers up while putting transactions into the table.

I.e starting from balance as 1000

• added new expense -10, subtotal: 990

• added new expense -45, subtotal: 945

and so on.

Overal balance: 945.

Following by that, would be cool to select several transactions and see their subtotal value.