ThermoPro TP18 Thermometers

This one is not designed to leave in the oven. You can just open the oven door, remove your food, insert the thermometer for a few seconds to get the reading, and return the food to the oven if it is not done.

I haven't had this problem. Mine had worked great. Maybe someone else had the problem.

You should use ice water as instructed in the manual.

It should lock on a specific temperature reading. You might want to contact the manufacturer because it sounds like something is wrong if yours continues to jump around.

Yes it will take the temperature of thinner items. It can be used to take the temp of stove top cooking well such as boiled frosting or candy.

I can see mine with trouble.