If a form is issued to an intending tenderer without having been so filled in as completed he shall request the office to have this done before he completes and delivers his tender." Then follow the conditions of contract of which condition No. 10 is material; it states "If the specification or estimates of the work provides for the use of any special description of materials to be supplied from the Engineer in Charge 's store, or if it is required that the contractor shall use certain stores to be provided by the Engineer in Charge (such materials or stores, and the prices to be charged therefor as hereinafter mentioned being so far as practicable for the convenience of the contractor, but not so as in any way to control the meaning or effect of this contract specified in the schedule or memorandum hereto annexed), the contractor shall be supplied with such materials and stores as required from time to time to be used by him for the purpose of the contract only, and the value of the full quantity of materials and stores so 760 supplied at the rates specified in the said schedule or memorandum may be set off or deducted from any sums then due, or thereafter to become due to the contractor under the contract, or otherwise or against or from the security deposit.