So you're using one of those little thermometers that you put on the shelf to make sure that your refrigerator is running at the temperature you set it at. Well, you're doing it wrong.
So here's the deal. When you put that thermometer on your shelf all you're doing monitoring the air temperature. The unit goes through defrost cycles and cooling cycles which means it's reading is going to go up and down indefinitely and ultimately give you very inaccurate results. The best way to monitor the temperature inside your refrigerator is actually to monitor the temperature of the food that's inside of it, and this can be a little bit difficult to do because you don't want to be taking your thermometer and sticking it inside all of your food products. So what do you do? Well, you do what you see here. You put inside a glass of water. Clear glass, clear water and you can clearly see the reading on the thermometer.
Here we have the unit set at 35 °F and clearly the thermometer is reading almost exactly 35 °F. The reason we do this is because the temperature fluctuations in the glass of water are going to be far less than the temperature fluctuations of the air inside the refrigerator. So stop playing mind games with yourself writing down the temperature of your refrigerator every 15 minutes and get that thermometer in a glass of water.
Lastly, if it's off by one or two degrees that's perfectly normal. Don't call for service.