The image shows a facsimile checkbook register with normal entries. Usually, one spouse will write most of the checks. This is probably the person in the marriage who pays most or all of the monthly bills. For the sake of illustration, assume it is the wife in this marriage who pays most of the monthly bills. The one who pays most of the bills will carry the "main" checkbook. Note the item outlined with the red box. The wife is subtracting $100 from the register in her checkbook to create an artificial transfer of funds to her husband's checkbook. She is also reducing the balance in her checkbook by this amount. No actual check was written. No changes take place in the account at the bank. This transaction takes place only on paper. But, it gives Carl $100 with which to work in the checkbook he carries.