anchor.diff:  
   Before we look at each scenario, let us understand how `charged amount` and `balance` are calculated. 
   
  -=== Charged Amount/Invoice Amount/Amount
  +
  +[NOTE]
  +*Note:* An invoice consists of one or more invoice items. Each invoice item is of a different type and its amount is either positive, negative or zero depending on the type. The invoice item `type` and `amount` heavily influence the `charged amount` and `balance` calculations explained in this document. It is therefore advisable to familiarize with invoice item type/amount by reading the https://docs.killbill.io/latest/userguide_subscription.html#components-invoicing-overview[subscription billing] document before proceeding further.
  +
  +=== Charged Amount
   
   The `charged amount` (also known as `invoice amount`, `invoice total` or simply `amount`) specifies the amount that the customer is charged as part of an invoice. It is computed by adding up the amounts on invoice items of type `FIXED`, `RECURRING`, `EXTERNAL_CHARGE`, `USAGE`, `TAX`, `ITEM_ADJ`, `REPAIR_ADJ`, `PARENT_SUMMARY` and `CREDIT_ADJ`. Note that `PARENT_SUMMARY` invoice items are only applicable in the case of https://docs.killbill.io/latest/ha.html[hierarchical accounts] and will be skipped in the rest of this document.
   
  
positive.code: ----             
  
  [start=2]
  . When the account is charged (either due to a recurring subscription or an external charge), the credit added is adjusted. So, for example, if an external charge is created for `$100`, it will have an invoice item of type `EXTERNAL_CHARGE` and amount `100`. In addition, it will also have an invoice item of type `CBA_ADJ` and amount `-20` automatically generated by the system corresponding to the credit adjustment.
  
  So, `CHARGED AMOUNT` and `BALANCE` are calculated as follows:
  
  
negative.code: 
  . Let us assume that an invoice is generated corresponding to a recurring subscription for `$100`. It will have an invoice item of type `RECURRING` and amount `100`. Assuming that the account has a valid default payment method, the invoice is automatically paid, so its `invoice balance` is `0`.
  
  . When this https://killbill.github.io/slate/#invoice-adjust-an-invoice-item[invoice item is adjusted], the invoice is modified. As before, an invoice item of type `ITEM_ADJ` and amount `-10` is added. In addition, another invoice item of type `CBA_ADJ` and amount `10` is added to bring the balance to zero. The addition of this positive `CBA_ADJ` item represents a credit generation by the system.
  
  So, `CHARGED AMOUNT` and `BALANCE` are calculated as follows:
  
  