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What do you think of the explanation about how the Doctor knew what was going on?

I thought it was very interesting information but I'm not sure if it is possible in real life.

I'm doing some major belief suspension. If he can only see one place at a time, he's been extremely lucky in his viewing periods. He's going to fall way behind in his work if he's busy being a voyeur.

Way beyond believable but I'm willing to accept it for the sake of the story

Suspended disbelief button has been activated. I do indeed hope all this is fiction.

I agree with Lynda, this is a very limited weapon if it can only be in one place at a time - hitting any particular scene at the vital moment would be very hit-and-miss. Good job Kensit has plans for Sentinel Mark II, with multiple screenings, :D