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There are all kinds of engine instruments available for use in a pod. Some are electric and others require no power whatsoever. This is a wet-bulb coolant temperature gauge that measures temperature based on pressure inside the capillary tube. The hotter the coolant temperature, the greater the pressure inside this tube. As pressure increases, the needle rises. When pressure (temperature) decreases, the needle drops. This runs directly to an engine and doesn't require electricity.