Setting "Uses Special Equipment" for a Service will block same service from being chosen again within any previously scheduled time period. In short the same service cannot overlap itself.
The patient can still schedule a different service which overlaps a service with "Uses Special Equipment" checked.
Click the All Tabs (Looks like a plus + sign)
Click the Services tab
Click the View "All" Go button to see all Services
Click on a Service
Check "Uses Special Equipment"