I got certified for decompression diving with my YMCA basic OW. They had these tables with 60 ft for 60 mins, 70 ft for 50 minutes etc. If you stayed longer the tables showed you how long you had to stay at 20 ft and how long you had to stay at 10 ft before you could surface.
My OW PADI course did the same thing, we used the Navy dive tables. On our 8th or 9th dive we dove to 130ft. No big deal.