Configuring Thresholds

Im having some trouble understanding Thresholds. Say for example i want to set up a Threshold for used disk space on my exchange server if i go to the edit monitor page when i can configure Thresholds it say:

'Threshold allow you to set safe limit for the data collected for graphs. OpManager can be configured to send notifications if the limit is violated'

and

'Threshold Limit (NUMBER) eg. 70 (or) 95 etc'

i dont understand the eg. 70 (or) 95 etc section? is this a value in MB? or KB? or Kb or what?

also same goes for things like active user logons threshold is the eg. what does the eg. 70 (or) 95 etc refer to?

thanks