The instrument shall be operated, maintained and cleaned in the manner specified by the manufacturer of the instrument, and each manufacturer of instruments for use in this method of testing milk for butterfat shall satisfy the director of agriculture that their instructions are complete and by following them an accurate test for butterfat will result. Except as provided below, instrument calibrations and operation shall be conducted only by technicians licensed by the department of agriculture specifically for this method using procedures for calibration and procedure checks, as recommended in the official first action approval published in Vol. 52, No. 2, 1969 of the Journal of the Association of Official Analytical Chemists or in the latest edition of the Official Methods of Analysis of the Association of Official Analytical Chemists.

(1) Samples used for calibration shall be prepared in the same manner as samples upon which producer payments are to be based. If composite samples are to be tested, the samples shall be preserved and stored in the same manner as the regular composites. If fresh samples are the basis for payment, then the samples shall be from fresh milk.

(2) Samples used for calibration shall include samples in (3%-4%) (4%-5%) (5%-6%) ranges.

(3) Temper all milk samples, whether fresh or composite to 98°-100°F. in thermostatically controlled water bath which is provided with an accurate thermometer: Provided, That a lower temperature which is proven to give accurate tests to the satisfaction of the director of agriculture may be used.

(4) When any sample differs in butterfat content by greater than 2.0 percentage points from the sample preceding it through the instrument, there shall be an immediate retest and the second test shall be the one recorded.

(5) Any dairy technician operating this instrument shall hold a license specifically for this method and shall also hold a Babcock testing license with the department of agriculture.