everyday, for example i was #1 in my niche one day and received 2000 hits from one keyword, now im again about 13 or 14
Depends on updates (changes) of Google in algorithm. Google is constantly updating their site....Especially minor updates that we don't see and the major updates that we obviously see...
im tracking it everyday.. I have different results everyday.. That's one main task of seo,"to maintain your rank" you can be number 1 today and all of the sudden lost tomorrow