Mouse scroll page jump problem

I had to rebuild my laptop and since reinstalling Reader, I have a problem with the mouse scrolling.

Previously when viewing a multi page document, I would zoom out to 1 page in window, then I could scroll the mouse and it would jump to page 2 then 3 (ie single page at a time).

Now when scrolling it jumps from 1 to 4, 7 etc (very annoying)!

I know of the continuous scroll etc but cant find the correct settings or somewhere to change the number of pages it jumps.

Many thanks in advance.

geo