Why this liquid filled expansion column earns its place
This is the thermometer that lives inside the cabinet rather than in your hand. A probe tells you about a piece of food at one moment; a cabinet thermometer tells you what the storage itself has been doing, which is the question when a fridge has been drifting overnight or a door has been propped during a delivery. The liquid-filled expansion column is the reason it is worth having as well as a digital probe: there is no battery to go flat unnoticed and no display to fail, so the reading is there whenever someone opens the door — including on the morning after a compressor has struggled, when nobody was watching.
The -20 to +40 °C scale is aimed squarely at chilled and frozen storage. It covers the +1 to +5 °C most kitchens run their fridges at, sits well clear of the 8 °C ceiling that chilled storage is judged against in UK kitchens, and reaches the -18 °C a freezer should be holding. Worth knowing where the bottom of that scale falls: -18 °C is comfortably on the dial, but a deep-store or blast cabinet running colder than -20 °C will bottom the column out and stop telling you anything useful. Placement decides whether the reading means anything at all — hang or stand it in the warmest part of the cabinet, which is usually high and towards the front, not tucked against the evaporator where the air is coldest and not in the door where it reads the room every time someone opens it. Read it before you open the door, not after, and write the number down on the same round each day so the record shows a pattern rather than a series of one-off numbers.
