gvim visual mode selection changes as you scroll up and down, how to fix it?

If I select a long patch of code spanning several pages, I'd like to view how much I actually selected by scrolling up and down. However this will automatically 'ruins' what I have selected because it changes the anchor!

How can I fix the two ends of what I have selected in visual mode? Many thanks.

--
--
You received this message from the "vim_use" maillist.
Do not top-post! Type your reply below the text you are replying to.
For more information, visit http://www.vim.org/maillist.php

---
You received this message because you are subscribed to the Google Groups "vim_use" group.
To unsubscribe from this group and stop receiving emails from it, send an email to vim_use+unsubscribe@googlegroups.com.
For more options, visit https://groups.google.com/d/optout.