Default Payment Method on a sales quotation

Can anyone tell me where you set up the default payment method for a customer?

When you enter a sales quotation, the field Payment Method on the Accounting tab can be set to a default value that the documentation says is taken from the Business Partner Master (customer record). However, I can't see anywhere on the BP Master to set a default value.

SBO 2005A SP01 PL18.

TIA

Douglas McDove