The maximum (MAX.) and minimum (MIN.) temperatures are the highest and lowest temperatures to have occurred during the past 24 hours. The AT OBSN temperature is the temperature at the time you take your observation. Enter to the nearest whole degree.
The minimum must be at least as low as the lowest of yesterday's and today's AT OBSN temperatures, and the MAX must be at least as high as the highest of today's and yesterday's AT OBSN temperatures. For example, if yesterday's AT OBSN temperature was 95, today's maximum must be at least as high as 95, even if the maximum this calendar day was only 86. You may record the 86 maximum in the REMARKS (far right) column as "PM MAX 86," as shown on the sample page [inside front cover] on the first day of the month. This is optional. See the REMARKS column on the sample page for the 23d of the month for recording last night's minimum (23), when it was warmer than yesterday's AT OB temperature (11).
MAXIMUM AND MINIMUM TEMPERATURE OBSERVATIONS - MAXIMUM-MINIMUM TEMPERATURE SYSTEM (MMTS)
If you have liquid-in-glass thermometers, please see paragraph 7(b). If you have the MMTS, obtain the maximum and minimum temperatures by pressing the buttons marked "MAX" and "MIN", respectively. Record these readings, as well as the current temperature, to the nearest whole degree. The current temperature is the reading shown when no buttons are depressed. If the reading to the right of the decimal is 5 or greater, round off to the higher figure; i.e., 39.5 should be recorded as 40. After recording these values on your form, press the "RESET" and "MAX" buttons simultaneously, then do the same with the "RESET" and "MIN" buttons. You can check to be certain the readings reset properly by pressing the "MAX," then the "MIN" buttons. They should read the same as the current temperature.
If the display reads "HELP," there has been an interruption in the power supply. To restore the MMTS current temperature reading, press the reset button only. You may still obtain maximum and minimum temperatures by pressing the appropriate buttons. However, if the power was off during an extended period, including the time the highest or lowest temperature occurred, the readings shown may not be the highest and lowest. If you believe this is so, you may write "Power failure during time of max (or min) temperature" 'in the "REMARKS AND NOTES" area of your observation form.
LIQUID-IN-GLASS MAXIMUM AND MINIMUM TEMPERATURES
MINIMUM TEMPERATURE. The MINIMUM thermometer should be read FIRST so that the index in the minimum thermometer will not be jarred or disturbed in any manner before the reading is made. It should be read while in its nearly horizontal or "set" position by reading the temperature scale at the end of the small index farthest from the bulb (the right hand side as you look at it). Do not reset the MINIMUM thermometer until the maximum thermometer has been read and reset. Reset the minimum thermometer by raising the bulb end sufficiently to allow the small index to slide to the end of the alcohol column, and then lowering the thermometer to its nearly horizontal position.
MAXIMUM TEMPERATURE. Lower the maximum thermometer slowly to a vertical position, with the bulb end down. Then, read the maximum temperature from the top of the mercury column. To reset it whirl it clockwise several times until the reading is approximately the~ same as shown on the minimum thermometer. Next, return it to its nearly horizontal position with the bulb end slightly elevated. NOTIFY THE SUPERVISING OFFICE if the maximum and minimum temperatures disagree by more than one degree after setting.
TEMPERATURE AT TIME OF OBSERVATION. This should be obtained by reading the maximum thermometer after it has been whirled and while it is still in a vertical position. The current temperature may be determined at other times of day by reading the end of the alcohol column of the minimum thermometer without disturbing it.