At approximately 0000, 0600, 1200 and 1800 UTC, the observer shall make a time check mark on the trace by raising the pen the width of two printed temperature intervals.

17-68.   CHANGING THERMOGRAPH/HYGROTHERMOGRAPH CHARTS

The observer shall change charts on 7-day thermographs on the 1st, 8th, 15th, 22nd, and 29th of the month, at 0800 LST, or as soon thereafter as practical, except stations obtaining hour temperatures from the thermograph for entry on MF1M-10C may change them on Fridays to conform with mailing instructions. Before placing the chart on the thermograph, the observer shall use a typewriter, rubber stamp, or pen and ink to enter the following data:

a.  In the upper left hand corner, or in spaces provided, enter the station name and type, meridian of local standard time, and on the first of the month, the time that the pen is touched.

b.  Across the top of 7-day charts at each noon line, enter the corresponding date.

c.  Above the point where the trace will begin, enter the dry-bulb temperature to whole degrees and the time of beginning to the nearest minute.

To change the chart, the observer shall move the pen aside with the shift rod and lift the cylinder until it is clear of the spindle. The observer shall wind the clock and replace the chart. The observer shall make sure that the bottom of the new chart rests against the shoulder of the drum and that the chart fits the drum snugly, with both ends under the spring clip. The horizontal lines should coincide where the ends overlap. Replace the cylinder on its spindle, and adjust the position of the chart for time and temperature before replacing the pen on the chart.

17-69.   ANNOTATION OF THE THERMOGRAPH CHART

After removing the used chart, the observer shall:

a.  Enter the time of any adjustment, an arrow indicating the point of adjustment, and the dry-bulb temperature, if adjustment other than that for time has been made.

b.  Above the end of the trace, enter the time of removal and the dry-bulb temperature to whole degrees at the time the pen was lifted from the chart.

c.  Enter above the time check lines, the difference (to whole degrees with proper algebraic sign) between the thermograph reading and the corresponding dry-bulb reading.

17-70.   THERMOGRAPH/HYGROTHERMOGRAPH TIME ADJUSTMENT

The observer shall adjust the chart for time by turning the cylinder until the pen point is slightly to the right of the appropriate time-arc line on the chart. The observer shall take up the play in the gear mechanism by holding the top edge of the cylinder lightly and turning it counter to the direction of normal rotation until the pen point indicates the correct time. The observer shall adjust the instrument promptly if at any time the record trace is in error by more than 30 minutes on a 7-day thermograph, or 10 minutes on a 1-day thermograph.

17-71.   THERMOGRAPH/HYGROTHERMOGRAPH TEMPERATURE ADJUSTMENT

When the chart is changed, the observer shall adjust the thermograph to the dry-bulb temperature, if necessary, by means of the adjusting screw located on an extension of the pivoted end of the sensing element. During the process, the observer shall tap the instrument lightly to eliminate transient frictional effects in the linkage mechanism. The observer shall adjust the instrument promptly if, at any time, the recorder trace is in error by more than 5 degrees. When it appears that the pen will pass off the printed divisions of the chart, the observer shall set the pen up or down equivalent to 10 degrees or 20 degrees by means of the adjusting screw, renumber the lines accordingly, and indicate on the chart the time of the adjustment. If, after adjustment to any intermediate temperature, the thermograph reads too low at the time of daily maximum temperatures, and too high at the time of daily minimum temperatures, the pen arm is swinging over too small an arc. To lengthen the pen arm, the observer shall turn the length-adjusting nut in the direction that moves the fulcrum to the left. Conversely, if the recorded temperature is too high at the time of maximum temperatures and too low at the time of minimum temperatures, the observer shall shorten the pen arm by turning the adjusting nut in the opposite direction.

17-72.   THERMOGRAPH/HYGROTHERMOGRAPH DISPOSITION

The station shall forward completed thermographs or hygrothermographs for the month, including the one ending at 0800 LST on the first of the following month, to the NCDC not later than the second working day of the following month. The charts shall be assembled in chronological order with the first day of the month on top.

17-73.   GENERAL MAINTENANCE OF THERMOGRAPH

Once a week, the observer shall remove any accumulation of dirt and grease. The observer shall use a soft cloth, or camel's-hair brush, to brush loose dirt from the Bourdon tube. If any foreign substance should stick to the tube, the observer shall remove it with a soft cloth dampened with water, alcohol, ammonia, or a suitable petroleum-base solvent. An abrasive cleaner shall not be used on the tube. If the plating on the Bourdon tube flakes off, the thermograph should be replaced.

17-74.  MAINTENANCE OF THERMOGRAPH CLOCK

The observer shall not remove the clock from the chart cylinder in which it is mounted. Repairs and cleaning should be done by a watchmaker, if practical. Otherwise, a replacement should be secured. During periods of extremely cold weather, thickening of the lubricating oil may stop the clock. To start the clock, it may be necessary to warm the clock to a temperature above freezing and to rotate it gently back and forth around the axis of rotation of the cylinder. If the clock has not been cleaned recently, a cleaning may restore normal service. Undue friction between the clock-driven gear and pinion may also stop the clock. If the clock gains or loses more than 2 minutes a day, the observer shall adjust the timing regulator. The observer shall open the small inspection plate in the top cover of the clock compartment for access to the adjusting lever. The observer shall move the lever toward F if the clock is losing time; toward S if the clock is gaining time. The observer shall make time adjustments when changing charts, if possible, to preserve the continuity of the record. When a clock gains or loses more than 10 minutes a day, the clock should be replaced unless it is practical to have it repaired by a local watchmaker. Replacement clocks are available from the National Logistics Supply Center (NLSC).

a.  The gears on replacement clocks have a number stamped on them and they will generally mesh satisfactorily with a gear-type spindle of the same number. If they do not mesh satisfactorily, the observer shall adjust the position of the pinion after loosening the three screws near the edge of the base of the cylinder. The spindle screws into the base on the gauge and in some cases may be secured by a wing nut. If accessory items such as a spindle, gear, pinion, washer, and wing nut are received with a replacement clock, the equivalent parts should be returned with the defective clock.

b.  The gear-type spindles are provided with a small, horizontal hole in the shaft to facilitate spindle removal with a spindle wrench or a short rod such as a nail. The friction between the gear and the shaft is enough to permit initial loosening and final tightening of the spindle by hand. The leverage afforded by the spindle should then be sufficient to permit removal or replacement by hand. The observer shall not use pliers or other metal tools on the shaft or gear. If the threads do not mesh readily, the observer shall request a replacement spindle.

c.  The gear should not be free to turn after the spindle is tightened. The observer shall make sure that the outer, beveled edge of the washer faces downward between the gear and the base of the gauge. The observer shall center the washer when the spindle is tightened in order that the gear will be properly secured between the washer and the shoulder of the spindle.

17-75.   MAINTENANCE OF THERMOGRAPH PEN

The observer shall fill the pen barrel not more than half full. The special ink used is moisture-absorbing and retaining because of the alcohol and glycerin in it. If, during periods of high humidity or prolonged periods of drizzle or light rain, the pen tends to overflow because of the water absorbed by the ink, the observer shall empty the pen barrel with a piece of blotter and refill. About once a month, the observer shall remove the pen and wash it thoroughly in warm water. The observer shall replace the pen if it becomes too blunt to draw a fine line. If the ink does not flow readily from the pen, the observer should draw a piece of hard, bond paper, or cellophane, between the nibs of the pen.