Date.new(2000,1,1).cweek should == 1
Date.new(2000,1,1).cweek, the result is 52.
My Ruby version is 2.1.1
#2 [ruby-core:62429] Updated by Andrew Vit about 2 years ago
This looks like correct behaviour. From a previous issue #9372:
A period of time of seven days within a calendar year, starting on a
Monday and identified by its ordinal number within the year; the first
calendar week of the year is the one that includes the first Thursday
of that year.