Maximum and Minimum temperatures from April to September

This thermometer is placed in the shade on our patio. Circumstances beyond my control mean that it has not been regulated since April 2018. I can't remember what the coldest temperature was in the depths of winter. I did think about cleaning it up but .....

How it works: The red button is pressed to re-set the thermometer. On certain models this can be done with a magnet too. The bend of the U contains a thread of mercury. Two scales are provided, one against each limb of the tube so that the temperature may be read against either of the mercury levels. Resting on each of the mercury surfaces are small steel indexes provided with light springs to hold them in position in the stem. Expansion or contraction of the mercury causes a movement of the mercury thread. Consequently, one or other index is pushed forward by the mercury and left in the extreme position reached. So yesterday's temperature was 20C, and the maximum temperature reached in the shade since April was 31C.