Measuring temperature question.

I have a question:

The textbook states "The metal in the evaporator is 10 degrees warmer than the refrigerant inside".

Later it's mentioned that superheat is the difference between the temperature you obtained from the tubing and the saturation temperature correspondent to the suction pressure that you obtained.

Why is the difference in temperature between tubing and the refrigerant inside not considered when calculating superheat?

My logic tells me that if the would have to subtract 10 degrees to the thermometer reading temperature from the tubing to obtain the actual refrigerant temperature before we can calculate superheat. But that is not mentioned anywhere in the book.

Thanks