Responsive web page with consistent line numbers on all screen sizes

Well i have no idea how to do that so i hope you can help me.
We are working on a digital text book and need to show line numbers.

The web page is fully responsive and there is no way to ensure everybody looking at one page has the same screen size. So if person A refers to a part of the text, person B must be able to find the text quickly.
With a paper book person A would say look at page 15, line 27.

In our book person A can say look at chapter 3... and has no way to specify the line number. Is there any way to get dynamic line numbers, so "line" 27 on Person A's Desktop is the same as "line" 27 on person B's smartphone?

Right now the only way i can think of is counting characters and define a ne "line" every 70 characters. With this counting you could then go on and include a visual marker next to the text to show that this is a new line.

Would be great if you guys knew a better way.