6418
Invar 36 has been used in aircraft control systems , electronic devices , optical instruments , and medical instruments that are exposed to significant temperature changes .
 Invar, control systems, optical, medical, temperature
Please list all entity words in the text that fit the category. Output format is "word1, word2". 
Option: manufacturing standard, machanical property, manufacturing process, material, engineering feature, process parameter, machine or equipment, application, process characterization, enabling technology, biomedical, concept or principle 
Text: {0} 
Answer:
 Invar, control systems, optical, medical, temperature