All using agencies, either by or with the authorization of the head of the department under which the using agency operates, shall file with the Purchasing Manager detailed requisitions or estimates of their requirements in supplies and contractual services in such manner, at such times, and for such future periods as the Purchasing Manager shall prescribe.
A using agency shall not be prevented from filing, in the same manner, with the Purchasing Manager at any time, a requisition or estimate for any supplies and contractual services, the need for which was not foreseen when the detailed estimates were filed.
The Purchasing Manager shall examine each requisition or estimate and shall have the authority to revise it as to quality, quantity, or estimated cost, but the Purchasing Manager shall consult with the head of the requisitioning agency prior to making revision.
