diff --git a/lib/page.js b/lib/page.js
index <HASH>..<HASH> 100644
--- a/lib/page.js
+++ b/lib/page.js
@@ -22,7 +22,9 @@ function test (opts) {
       .get(opts.url)
       .then(() => {
         if (opts.scroll || opts.reporter === 'fps') {
-          return session.execute('var dir=-1;function f () { window.scrollBy(0,dir*=-1); window.requestAnimationFrame(f); } window.requestAnimationFrame(f);');
+          const scroll = (typeof opts.scroll === 'number') ? opts.scroll : 10;
+          const iterator = opts.scroll ? 1 : -1;
+          return session.execute(`var dir=${scroll};function f () { window.scrollBy(0,dir*=${iterator}); window.requestAnimationFrame(f); } window.requestAnimationFrame(f);`);
         }
       })
       .then(() => {
Allow for customisable scrolling behaviour

If fps reporter is specified with no scroll parameters then stick with present behaviour of oscillating by 1 pixel. Otherwise if scroll option is provided then scroll continuously by the amount specified, or <I> pixels at a time if a non-numerical value is passed.