What's wrong with my Amazing Clock??

I got this clock on my wall, wow what a clock. Really. When I get the Right Answer to this PizzaQ, I will give you the URL so you can have this clock, too.

Its big ballyhoo selling point is Accuracy. Like totally scary Super Accuracy. (And Germans designed it, so it looks way cool too, muy butch. Maybe the Germans built it but hired an Italian to design what it looks like.)

But there's Something Really Odd about my clock.

Every time I take it with me into the past in my Heathkit Time Machine (the TM-212, boy was THAT a hard kit to build!), I take a perfectly fresh Energizer Bunny battery, but if I travel to the 19th Century or earlier, MY CLOCK JUST DOESN'T WORK!

But then I come home to 2005 and the damn thing works like a Swiss watch!

Oh -- okay, well, I traveled Forward in time last week, to see Halley's Comet come back in 2062, and my Amazing Clock worked just fine!

(I shouldn't reveal stuff about the Future, but you would not believe what men and women are spending their money on with plastic surgeons in 2062!!! And Jeez! You should see who just broke the Major League Home Run record! Hint hint hint: There's a new baseball superstar they call "Babe." End hint.)

Okay now, besides the usual Vleeptron PizzaQ No-Surfing Honor System, A Certain Person who hangs here is ineligible to answer this PizzaQ. You know who you are.

Why doesn't my Amazing Clock work when I travel back in time?

2 slices. I'm not sure if this is Easy or Hard.

Oh, PS: Heathkit went out of business in 1992. So I have the TM-212, and you don't, eat your hearts out. I know how the jury is going to decide the Michael Jackson thing. Hahahaha.