Hello @Tinn_Vision , thank you for your question! The error you are seeing is caused by the type of property you are attempting to observe. An Entity's position is represented by the type SIMD3 , while its orientation is represented by the type simd_quatf. For SIMD3, x is a stored property, while for simd_quatf, angle is a computed property. This means the slider would have no way of setting the value of angle when a person slides the handle. For this reason, I would consider the error you are seeing to be expected behavior. You can review the Swift documentation for properties for more information. simd_quatf is a Quaternion, and while the implementation details are complex, it does not store values like the number of degrees the entity has rotated around an axis. If you'd like to make a slider that spins an entity around the Y axis, for example, you'd need to store that observed slider value someplace else, and then convert that value to a rotation, depending on what you need for your app. I'd be h