I'm tracking (every hour) one of my client's apps which is listed in one of the category charts (not the overall charts). However I noticed strange ups and downs in the chart positions. Within only some hours the app hikes down (e.g. from place 60 to 150) and goes straight up to 60 again (I think when someone makes a download).
It seems like other apps surrounding the tracked one are much more constant in their positions (especially the Top 50 ones). Is there any explanation for this?