"This experiment has been continuing for four weeks."
Translation:Bu deney dört haftadır devam ediyor.
This suffix looks exactly like the "statement of fact" suffix but has a different meaning. When you are talking about a period of time that is still continuing, you must use the -DIr suffix. For example "Ben beş senedir Türkçe öğreniyorum" "I have been learning Turkish for 5 years." :)