var UpdateInterval = 1;
var PixelPerInterval = 1;
var scrollerInterval;

function start_scroll_up1() { scrollerInterval = setInterval(scroll_up1, UpdateInterval); }
function scroll_up1() { document.getElementById('scroller1').scrollTop -= PixelPerInterval; } 
function start_scroll_down1() { scrollerInterval = setInterval(scroll_down1, UpdateInterval); }
function scroll_down1() { document.getElementById('scroller1').scrollTop += PixelPerInterval; }
function scroll_reset1() { document.getElementById('scroller1').scrollTop = 0; } 

function start_scroll_up2() { scrollerInterval = setInterval(scroll_up2, UpdateInterval); }
function scroll_up2() { document.getElementById('scroller2').scrollTop -= PixelPerInterval; } 
function start_scroll_down2() { scrollerInterval = setInterval(scroll_down2, UpdateInterval); }
function scroll_down2() { document.getElementById('scroller2').scrollTop += PixelPerInterval; }
function scroll_reset2() { document.getElementById('scroller2').scrollTop = 0; } 

function stop_scrolling() { clearInterval(scrollerInterval); }