The meaning of visit count on admin’s bar

What is the exact meaning of the number that appears when I hover stats graph at admin’s bar:

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For example, right now I can see 9 on one of my sites. And when I click it, I can see following numbers of visits per past days:

  • today — 26
  • yesterday — 80
  • the day before yesterday (April 1st) — 98
  • March 31st — 131
  • March 30th — 99
  • March 29th — 118

and so on — there’s no “nine” among these numbers.

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I am asking, because it never shows anything accurate or recognisable for me neither for any day nor for any of my blog network’s sites. And I don’t know how to interpret this number.