Numbers under bass notation...

[xanatizer]

Hi! So I just got a copy of Tom Wolk's "Rock Riffs for Bass" and there are numbers written below the notes, under the stave. I tried to find answers online and the nearest thing that comes up is figured bass. Since this music is 20th century rock, I'm guessing it isn't figured bass. So what is it?

 

[FatStringer52]

Fretting fingers.

 

[xanatizer]

Fretting fingers.

Thanks! That was one of my guesses, but the zeros are what really confused me. Phantom finger?

Anyway, that doesn't seem like info I'd use, seeing as I'd just fret it as it made sense to me.

 

[FatStringer52]

0 = Open string.