The Stevenson screen containing 4 thermometers and a thermo- hygrograph is located about 100 metres east of the INT Dome. The rain gauge is a few metres to the north-east of the screen and is normally kept locked. The replacement charts for the thermohygrograph are kept in the cupboard in the TO Office and are changed every Monday morning by the TOs.
On rare occasions it may be necessary to read the rain gauge. This is usually done on the first day of the month.
Open the bottom flap of the rain gauge using the Yale key. Take care because the measuring cylinder is only resting inside and is not fixed in any way. Remove the cork from the nozzle and operate the valve to let the accumulated rainwater run out. Quite often, the volume will be greater that the capacity of the measuring cylinder so the valve must be closed before the level of the water reaches the 10.0 mm mark. NOTE THAT THE MAXIMUM READING IS 10 AND NOT 100 MM. Record the reading each time until a pink, viscous liquid comes out. This liquid is intended to prevent evaporation and it is less dense than water. Wait until it has settled out on top of the water and take the reading at the bottom of the liquid mensicus. Note the reading, adding it to the others (if any), empty the cylinder and cork the nozzle. Replace the cylinder, lock the gauge and record all readings along with the time of observation on the ICONA form.