Answers: they take a small amount of the TB reactor contained by small syringe with a small nozzle & create a small red bump under the top layer of the skin. Then in 48-72 hours they look to see if the red-looking area get bigger or goes away. If larger, afterwards you have be exposed to TB & will need an Xray to show whether you enjoy it or not & will no longer have to do the theory test every year, just the Xray, if red nouns stays same or goes away, consequently you have not be exposed.
RN
they grab a nozzle and stick it in your arm, after check to make sure it doesnt acquire bigger and give you some impetuous looking thing on your arm, a touch redness is ok.