let h;
switch (window.orientation) {
  case 0:
    h = "portrait";
    break;
  case 180:
    h = "portrait-upside-down";
    break;
  case -90:
    h = "landscape-clockwise";
    break;
  case 90:
    h = "landscape-counter-clockwise";
    break;
}

window.addEventListener("deviceorientation",
  function(a) {
    switch (h) {
      case "portrait":
        (I = Math.round(100 * a.beta) / 100 - 30),
          (F = Math.round(100 * a.gamma) / 100);
        break;
      case "portrait-upside-down":
        (I = -1 * (Math.round(100 * a.beta) / 100 + 30)),
          (F = (Math.round(100 * a.gamma) / 100) * -1);
        break;
      case "landscape-clockwise":
        (F = (Math.round(100 * a.beta) / 100) * -1),
          (I = Math.round(100 * a.gamma) / 100 - 30);
        break;
      case "landscape-counter-clockwise":
        (F = Math.round(100 * a.beta) / 100),
          (I = -1 * (Math.round(100 * a.gamma) / 100 + 30));
        break;
    }
  }
);