your regular utility time machine for the mundane task of showing what happened last year. It turns out, people missed some stuff, and they would like to know - after the fact. They will pay. There will be lots of them. There will be an army of people operating the machine. What changes when you really know what happened last summer? What is the use of a machine that can tell you what happened last week, but can't tell you what is happening right now?
(from review of Time Machine by Andrew McCall)