A written document between the owner and the contractor signed by the owner and the contractor authorising a change in the work or an adjustment in the contract sum or the contract time. A change order may be signed by the architect or engineer, provided they have written authority from the owner for such procedure and that a copy of such written authority is furnished to the contractor upon request. The contract sum and the contract time may be changed only by a change order. A change order may be in the form of additional compensation or time, or less compensation or time (known as a deduction from the contract); the amount deducted from the contract sum by change order.