[Kanegasi]

Stats may not be available right at login. Plus, they could change with procs and other events during play. Use the event COMBAT_RATING_UPDATE instead. This could get spammy in a group, so you may have to check the unit return.

c:SetScript("OnEvent", function(self,event,unit)
    if unit=="player" then
        crit = round(GetCritChance(), 3)
        c.text:SetText( "Crit: " .. crit )
    end
end)

I just noticed that you're getting crit only once, which explains the 0 since you're getting crit before you even login. The OnEvent is just setting the same number over and over again if you use the event I suggested. I put another crit= inside the OnEvent for you. You can even skip using a crit variable and just put the round() call in directly.

c:SetScript("OnEvent", function(self,event,unit)
    if unit=="player" then
        c.text:SetText( "Crit: " .. round(GetCritChance(), 3) )
    end
end)