343. Express provision.

The architect or engineer may be given power to value additional or omitted work and to add the sum arrived at to, or deduct it from, the contract sum. Generally the contract will provide that additional work of similar character to, and executed under similar conditions as, the contract work should be valued at the rates and prices contained in the bills of quantities or schedule of rates1. Where there is no appropriate rate in the bills of quantities or schedule of rates, the architect or engineer may have power to adjust the rates provided or to fix a