A useful log records comparable readings and the circumstances around them. A list of numbers without dates, positions or recent door activity can make a normal change look like an unexplained fault.
What the observation tells you
Note the selected setting, thermometer location, time and whether shopping was recently added. Separate a settled observation from one made during cleaning or unpacking. If someone changes a control, write that down rather than silently starting a new series. There is no need to collect an elaborate minute-by-minute record that keeps the door open and disturbs the cabinet.
A useful next step
Take brief readings using the instrument's instructions and keep the same measurement position. Give the engineer the simple timeline, including any alarms or power interruption. Monitoring is not a reason to leave vulnerable food in inadequate storage; move it appropriately while an ongoing cooling concern is assessed.
Manuals and supporting guidance
Model-specific instructions take priority. These references support the practical principles discussed here; they do not diagnose your appliance.