When only some part of the day fits to screen, there is no visual indication of events that are hidden. Suppose you can directly see only 9:00 - 16:00 and you have event at 8:00 and 18:00, I'd like to see something like this in that case:

      | [^ more events]
 9 00 | 
<snip>
16 00 | [16:15 event]
   30 |
17 00 | 
      | [v more events]

Two notes to this proposal:

1. I guess that if there are no events at the very top and very bottom rows, placeholders could be displayed at them in order to save screen real estate.

2. if the event(s) description(s) fit into the row, they could be displayed right away (sorted by time) instead of placeholder.

IMO, implementing this should not be too complex and it would tremendously increase usability of calendar.