Rookie question about base+ times

This has possibly been asked before but I could not find it. I am new to master's swimming and some coaches have given us workouts based on our 100 time. It usually reads something like: 6x200 on base + 10. But different coaches have defined this differently. I have been told that I should take my sustainable 100 time which means 10-20 sets with 10 seconds rest in between and consider that my "base" So if I can swim the 100 in 1:25 and as long as I get 10 seconds rest I can continue, does that mean my base time is 1:35? If so, what does the workout first mentioned mean? I had one coach say swim each 200 at your base time + 10 seconds per 100 of the set (i.e. 1:45 + 1:45 so 3:30 for the set) and another has said swim your base time and add 10 seconds of extra rest at the end of the set (i.e. 1:25 + 1:25 + :10 so 3:00 for the set). Can anyone clarify what the whole "base +" terminology means and how it works? Or direct me to a good site that explains it in detail? I appreciate all the help as I try to improve myself. Thanks!