It is simply a graphic to show you how your drive if functioning. On your colored graph to the left you have blue lines and yellow sprays. The numbers to the right are using the same colors but in actual numbers rather than a graphic. Hard drives often have slower response rates when you get near the end of the drive. The numbers to the right indicate your best and worst results for the transering of data as well as an average number. The access time reference simply gives you an average of the drive's performance. Unless you are a true geek, you can disregard the Health tab unless you see something that fails (shows as something besides "Ok" in the Status column.