When finish a task/appointment, you can mark complete it

Mark complete is a special function of
eReminder. When a task or appointment is finished, you can flag it by
marking complete. This utility will give you a clear view to identify which
appointments/tasks have been done and which appointments/tasks you still have.

• To mark complete an appointment
  
• Select View->Current View->Day/Week/Month/Year,
  move mouse to the appointment you want to mark complete, right-click your
  mouse, and then select Mark Complete item in the context menu. The
  appointment you selected will be marked with completion flag.
  
• Or double-click the appointment you want to
  mark complete, in the Edit Appointment Entry dialog, click the
  Mark Complete button. The appointment you selected will be marked with
  completion flag.
  
• To mark complete a task
  
  
• Select a task and right-click your mouse,
  then select the Mark Complete item in the context menu. The selected
  task will be marked with completion flag.
  
• Or double-click the task you want to mark
  complete, in the Edit Task Entry dialog, click the Mark Complete
  button. The task you selected will be marked with completion flag.