Carol B. wrote:
Many elliptical machines can measure heart rate. Have you tried that and compared it to what your watch reports?
You could even use it as a real-time diagnostic tool to evaluate how wristband fit, sensor placement, and/or various arm movements affect relative precision between the two. They might not not match exactly, but you would want to see fairly close agreement plus correlation in trends.
Edit: You could/should calculate your heart rate manually too. No need for NIST - you come equipped with your own gold standard! 🙃 In all seriousness, tho, doing that would let you know if the elliptical sensor is reliably accurate.