A German customer who calls a plumber without agreeing on a price still owes a definite amount. Section 632 of the Civil Code fills the gap. If a fee schedule exists, the scheduled fee counts as agreed. If none exists, the usual fee counts as agreed. The written estimate, the Kostenanschlag or Kostenvoranschlag, is free unless the parties agreed otherwise. Section 649 covers the case where the estimate turns out too low. If the work cannot be done without a substantial overrun, the craftsman must tell the customer without delay. The customer may then end the contract and pay only for the work done so far. The Frankfurt Chamber of Industry and Commerce explains that an overrun of 10 to 20 percent is probably not yet substantial.