MS Windows Excel linking data from different files

I am trying to make a excel file that would contain all of the information from other 6 or 7 excel file. To briefly describe the situation, I want to have one main excel file that shows calander, and other 7 files has same calanders as well, for each department. So that when supervisors from each department puts in a employee that is out on one day, they would put it in their own excel file with calander, and it would also make changes to main excel file. I was able to make link from one auxilary excel file to main by using “=[test1.xls]CALANDER!I7” formula. However, I can’t find a way to make link to it from 6 other excel file to the main excel file. Can someone please help me out?