how to interpret the test charts

[Valter]

Hello everybody
i did a search but i didn't find,
you can explain the meaning of cd-r tests when you use Nero CD DVD for benchmark and disc quality and Speed and Opti Drive.
Yes I understood that a low number of errors is better,
often, during the same test I see 2 ~ 3 different graphics and don't understand what has been changed to get that.
if you can explain the settings used for testing and to achieve what, and what the ideal graph would be.
Many thanks.