.top);

    // Create a clipped rectangle - anything we draw will be constrained to this rectangle.
    // This prevents the occasional pixels from curves near the edges overrunning and creating
    // screen cheese (that phrase should need no explanation).
    context.beginPath();
    context.rect(0, 0, dimensions.width, dimensions.height);
    context.clip();

    // Clear the working area.
    context.save();
    context.fillStyle = chartOptions.grid.fillStyle;
    context.clearRect(0, 0, dimensions.widt