I'm having a problem with onPartialUpdate() drawing over itself without clearing

I put the basics of my source code below. It works great at first. But after 15 seconds or so (until onPartialUpdate() is called?) it starts to draw over itself.  I haven't figured a good way to debug it yet as it only seems to happen when I load the app on my watch. Is there a way to only clear a single drawing? Any advice would be awesome.

function onUpdate(dc as Dc) as Void{

    dc.setColor(Graphics.COLOR_BLACK, Graphics.COLOR_BLACK); //Set background
    dc.clear();

    /*
        Here's where the ticks, hour hand, and minute hand are calculated and drawn
    */
    
    onPartialUpdate(dc);

    /*
        Other things I want drawn on top of everything
    */
}

function onPartialUpdate(dc as Dc) as Void {

    /*
        Here's where the second hand is calculated
    */
    
    dc.drawLine(secXCoordFrom, secYCoordFrom, secXCoordTo, secYCoordTo); //Draw Second hand
}