u/Denator04

I was rewatching the first movie and when doc was talking about how the time machine worked, I got kind of confused, because he mentioned traveling to see the birth of christ which is in the year 0000; but is it possible to go beyond that? There doesn't seem to be a switch that allows it to imput a date in BC, only AD. I'm only familiar with the movies and know nothing about other material, is this explained in a comic book or something?