If the solar rays fall on the thermometer, mounted outside window frame, it heats up and shows… its temperature, not the ambient air.
To avoid this, protect the thermometer shade cover that can be cut from a suitable plate an opaque plastic (e.g. from a milk bottle) or foam containers: they will take over the sun’s rays.
Recommend to read
TRACTOR-GARDENER
That's already more than a dozen years G. Malakhov works as the chief mechanic tool shop of one of Moscow's aircraft factories. But even more time (13 years) he is engaged in Amateur...
WOODEN GRASSHOPPER
Recumbent I've collected over the ten days together with their children and we called him "Grasshopper". Rear wheels have "Grasshopper" — from Bicycle "the Schoolboy one of which is...