You need to use a phone camera. Either get this web page up and scan the QR code
or
Start here with your phone
https://gphxhealth.gprpm.com/basic_info.html
I don’t know if it works using a laptop camera.
I was standing up it said my HR was 69 when it was about 67. I will try it lying down when my HR is likely to be 53 later on.
It came out with an HRV that I thought was a bit high (81, its more like 63)
Edit:
I have just tried it with my laptop camera. Fitbit says my HR is 53 and gpheart says 51.
I must admit I am impressed by this.
I have done another test lying in bed fitbit says 53 omron 54 and gpheart 53. This was using my phone camera.