If you know how cold it is inside your refrigerator, you can perhaps troubleshoot an electrical or mechanical failure in time to save the box’s contents from spoiling. A thermometer inside the box doesn’t tell you anything unless you open the box and check it. That’s why I like to use a wireless indoor/outdoor thermometer of the type that’s readily available in most hardware stores. I put the sending unit inside the box and mount the display monitor where I can easily see both the refrigerator and cabin temperatures. By moving the sending unit around inside the box— including the freezer compartment—I learn the characteristics of the refrigerator. If there’s a circulating fan, for example, it might be 10 degrees warmer in one corner of the box. Since items like fresh vegetables do better in slightly warmer temperatures, I know where to store them.