Chest freezers will always over-shoot the set temperatures. This is because once it hits the desired temperature there is still unevaporated refrigerant in the coils, which will evaporate and cause more cooling. If there is little or nothing in the chest, the temperature over-shoot will be large. A full freezer will be much more stable.
Remember one unassailable statistic, as explained by the late, great George Carlin: "Just think of how stupid the average person is, and then realize half of them are even stupider!"
"I would like to die on Mars, just not on impact." Elon Musk