Book Reports / Identifying Line Numbers in Shakespearean Plays [2]

Hi,
I'd like to know what the secret is to identify line numbers in King Lear.

Here's an example of what I find in the text:

"You heavens, give me that patience, patience I need!" 460
You see me here, you gods, a poor old man,
As full of grief as age, wretched in both: [270]
If it be you that stirs these daughters' hearts
Against their father, fool me not so much
To bear it tamely; touch me with noble anger, 465"

Why two sets of numbers that follow the text and which one is the line number?
Also, they most often don't reflect the physical number of lines that have passed on the page. I can count down 11 lines from 475 and that brings me to 485. Sometimes more, sometimes less. I tried counting blank lines, not counting them, counting and not counting lines that have only a character name and no line. I can't seem to find the secret to identifying lines exactly and I'd like to know how so that I can reference them accurately in my essay.

Thanks,
Brendan.