Hello, let’s talk about the temperature of your oven first. Generally, the preheating time is from turning on the oven until the tube is heated to red, and then the tube goes out. This is a heating process. If the jar goes out If the temperature dropped is 150 degrees, then the temperature indication temperature is not 150 degrees. The temperature after the second heating is the actual temperature of the oven, because the oven temperature reaches the normal temperature after the first heating. The temperature after the second heating is the standard temperature. Do you understand this explanation? And the thermometer doesn't reach the temperature you want all at once, it has to go slowly. Another problem is that the empty box is different from when you put things in it. For example, the temperature of the empty box is 150 degrees, and the temperature inside the box where you put the things is lower or higher. The temperature inside the box depends on the temperature you put it in. It depends on the temperature of the thing, so the temperature will change after putting it in the box.