Answer:
These are becoming obsolete. These have mercury unit inside. The mercury unit has coil inside that expands and contracts according to the temperature level outside. However the accuracy of their temperature reading falls short of digital counterparts. Also the purchase of products containing mercury has been restricted or banned in many states. However you can chance upon some models even today. And they cost much less than digital thermostats.
-
Replied By:
Richard Baker
(Burlington, VT)
-
Replied Date:
10/17/2016