At the time of writing there are three ‘Main’ versions.
- Excell version (the original one is not working on Mac): Training guidance tools using the API - #61 by MedTechCD
- Google sheets version (has some bugs): Recreate ithlete rHR/HRV chart? - #216 by Olly_Thomas
- Matlab version working on all phones and desktop browsers: How to - ImReady4 app for HRV guided training
My advice would be to use the Matlab version, which has best compatibilty.
Edit: changed the link to the Matlab version to point to the guide post.