Ok, I will add my 2 cents:

I was working on a way to create a function (set of functions) that would rotate an image so that it is always perpendicular to the ground.

Here is a beta version of a watch Iâ€™m working on, that will use it: Mellin - URWERK UR-T8 - watch face for Apple Watch, Samsung Gear S3, Huawei Watch, and more - Facer

Here is my newest result:

You will need 4 copies of the same image.

Here are scripts for their rotation and transparency:

for 1 and 8 octants

rot

```
(((((accelerometerRawY())*(accelerometerRawX()))/(((accelerometerRawY())*(accelerometerRawY()))+(0.28125*(accelerometerRawX())*(accelerometerRawX()))))/pi)*180)
```

trans

```
$((accelerometerRawY())/(accelerometerRawX()))>1||((accelerometerRawY())/(accelerometerRawX()))<-1&&(accelerometerRawY())>0?100:0$
```

for 2 and 3

rot

```
((((pi/2)-(((accelerometerRawY())*(accelerometerRawX()))/(((accelerometerRawX())*(accelerometerRawX()))+(0.28125*(accelerometerRawY())*(accelerometerRawY())))))/pi)*180)
```

trans

```
$((accelerometerRawY())/(accelerometerRawX()))>-1&&((accelerometerRawY())/(accelerometerRawX()))<1&&(accelerometerRawX())>0?100:0$
```

for 4 and 5

rot

```
(((pi+((accelerometerRawY())*(accelerometerRawX()))/(((accelerometerRawY())*(accelerometerRawY()))+(0.28125*(accelerometerRawX())*(accelerometerRawX())))))/pi)*180)
```

trans

```
$((accelerometerRawY())/(accelerometerRawX()))>1||((accelerometerRawY())/(accelerometerRawX()))<-1&&(accelerometerRawY())<0?100:0$
```

for 6 and 7

rot

```
((((pi/-2)-(((accelerometerRawY())*(accelerometerRawX()))/(((accelerometerRawX())*(accelerometerRawX()))+(0.28125*(accelerometerRawY())*(accelerometerRawY())))))/pi)*180)
```

trans

```
$((accelerometerRawY())/(accelerometerRawX()))>-1&&((accelerometerRawY())/(accelerometerRawX()))<1&&(accelerometerRawX())<0?100:0$
```

If you want to know, whatâ€™s going on in there, check out this: http://www.embedded.com/design/other/4216719/Performing-efficient-arctangent-approximation