In the last verse we are introduced to a period of time described as
a week.

 
  Daniel 9:27  And He shall cause to prevail a great covenant
               one week. And in the middle of the week He shall
               make cease sacrifice and offering and upon an
               extremity abominations, a desolator up until a
               complete destruction. And as decreed she shall
               be poured forth on the desolator. 

This week is singular!


It is NOT one of the 70 'weeks'!


[ As previously discussed each of the 70 'weeks' represents a series
  of weeks. ]


The key to understanding this 'week' is to realize,

The verse does not introduce any new details. It just summarizes the major
periods and events referred to in the prior three verses.  


It is this understanding of verse 27, which enables the nature of the
'week' to be defined.

      The start  - represents the beginning of the 70 'weeks'.

      The middle - represents the end of the 70 'weeks', which
                   corresponds to when Jerusalem is struck,
                   when sacrifice and offering cease.

      The end    - is the time of the demise of the future
                   ruler.

                   




This week is lopsided! The first half long (ie 3,500 years) and the
second half short.

This unusual arrangement explains the use of the word 'extremity'. The
period of abominations (the second half of this week) is in reality the
final finishing edge of the time encompassed by this week.

 [ NB: The book of Revelation, in chapters 11 and 12, also depicts
       this lopsided week. ]




The covenant is the holy covenant and upon expiry of the 'week'
those due to inherit the Kingdom will receive it.


   Note: It is God who causes the great covenant to prevail and it
         is God who raises up the desolator and brings judgment on
         'Old Jerusalem' and its sanctuary!