Hi Dru,
Allison is correct. The OB means "Overbooked" and there are multiple patients on that time slot. That is why you cannot just double click on the appointment slot to pull a chart, as the system does not know what patient to pull.
To access the chart, just click the providers name at the top of the schedule to go to detailed view. This will separate patients out all on their own lines allowing you to double click and pull the chart. In this detailed view you can also see who booked the appointment, and what day and time the appointment is booked for.