I've never known a mercury (Style) thermometer to be off, but maybe I'm wrong. It also has a built in hygrometer, and it is $3 from Home Depot.
Here is the link, the SKU# is 816799 in case the link doesnt work
http://www.homedepot.com/h_d1/N-5yc...splay?langId=-1&storeId=10051&catalogId=10053
Here is the link, the SKU# is 816799 in case the link doesnt work
http://www.homedepot.com/h_d1/N-5yc...splay?langId=-1&storeId=10051&catalogId=10053