code: function paintMarker(ctx, location, xRatio, color) {
    if (xRatio < 0 || xRatio > 1) {
      return;
    }
  
    const y1 = location.y;
    const y2 = y1 + location.height;
    const x = location.x + Math.floor(xRatio * location.width);
  
    ctx.beginPath();
    ctx.lineWidth = 1;
    ctx.strokeStyle = color;
    ctx.moveTo(x, y1);
    ctx.lineTo(x, y2);
    ctx.stroke();
  }
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