Slides from nowhere

Hi

I am starting to learn peices with slides in them that do not have a starting position. These can be either up or down. How do you play these? Where is the slide meant to start?

I tried to attach a pic but cloudflare blocks me.

Thanks in advance

The tab shows a slide from 10 fret on the B string down to 7 fret on G. But no note on g to start the slide.

Are you in the A minor pentatonic? Going from A to D puts you right in the middle of this scale. 

I would use my ears, but probably just sliding up from the 10th to the 5th fret on the B string would allow me to slide from the 5th to the 7th on the G string. And I would be in the scale the whole time.