electroencephalography (EEG), electrocardiogram (ECG), pulse oximetry, airflow, and leg movements. Sleep stages are assigned by human experts based on visua...

https://www.apple.com/jp/healthcare/docs/site/Estimating_Sleep_Stages_from_Apple_Watch_Sept_2023.pdf

, but restricted by their 4K limitation, size, 
 weight, and incredibly high price points that limit their usability to a very 
 select group of professiona...

https://www.apple.com/jp/pro-display-xdr/pdf/Pro_Display_White_Paper_Feb_2020.pdf