A delta threshold monitor measure the change, for example a change of X GB on a driver during Y minutes or a change of X procent during Y minutes. Here is a short step by step guide

1. In the console, under Authoring, Management Pack Objects, Monitors, create a new monitor
2. Choose to create a new unit monitor, Windows Performance Counters/Static Thresholds/Single Threshold/Delta Threshold, click next
3. Input a rule name and choose rule target, choose Availability as parent monitor, click next
4. Click browse a choose a object, for exampleObject: LogicalDisk
   Counter: Free Megabytes
   Instance: C: 

   Specify the interval and then click next

5. Enter a threshold, for example 100 for 100Mb. Click next
6. On the Configure Health window, click next
7. Check “Generate alert for this monitor”, input a alert description, click Create

This monitor will generate an alert if someone add or remove 100Mb on C: during 15 minutes (default value).