The allowance for credit losses is our best estimate of the amount of probable credit losses in our existing accounts receivable. We determine the allowance based on historical write-off experience, specific customer collection issues, the aging of our outstanding accounts receivable, and the credit quality of our customers. In determining our allowance for credit losses, we also consider current conditions and forecasts of future economic conditions and their expected impact on collections. Balances are considered past due based on invoiced terms. Account balances are charged off against the allowance after all means of collection have been exhausted and the potential for recovery is considered remote.