Thermometers are mounted in instrument shelters on supports. The longer shaft holds the maximum thermometer, while the shorter holds the minimum.. A pin in the minimum thermometer shaft prevents it from rotating more than a quarter turn (about 90^o). It is reset by rotating it to the vertical position.

Thermometers are read and recorded to the nearest whole degree.  Below zero temperatures are recorded with a minus (-) sign to the left of the digits; i.e., -15 for 15^o below zero. The thermometers should be reset after they are read. Readings should usually be recorded on WS Form B-91

Lline of sight from your eye to the top of the mercury or alcohol column needs to be level. If not, the reading will be too high or too low.

The highest temperature occurring since the maximum temperature was previously set is the reading at the top of the mercury column, taken with the bulb end lowered.

The maximum air temperature is hard to read on the thermometer . Rotate the position you are looking at the thermometer until you can see the mercury column. The example below reads 43 F. 

After reading and recording the maximum temperature on the B-91 form, spin (rotated) by hand the thermometer to reset the mercury column to the current temperature. The maximum temperature is recorded on the day of observation on the form even though the maximum temperature occurred the previous day if the reading is taken at 7:00 AM .

The minimum temperature is the reading at the end of the index farthest from the bulb (not the reading on the alcohol column).

Read the thermometer before moving it from the almost horizontal position in which it was set at the time of the last observation. Record the information on the B-91 form. The minimum temperature is 68 degrees.

To set the minimum thermometer, point the bulb end upward . Allow the index to fall to the end of the alcohol column. Then turn the thermometer counterclockwise until it stops. The bulb end will now be slightly lower than horizontal.

Read the current temperature from the maximum thermometer while it is in a vertical position after spinning. Read the temperature at the end of the mercury column farthest from the bulb.

After recording the temperature and rainfall data on the form , enter the data into the ROSA system by phoning the ROSA computer and using the touch tone phone enter the numbers. This information will become part of a computer feed generated by the NWS that is captured and displayed by the Regional and National Climate Data Centers.  If the weather station includes an evaporation pan , then the temperature information is recoreded on a B-92 form