Indeed, this app produces more or less the same output. I'm not convinced by the wrist measurement approach because they tremor doesn't affect my hands and arms noticeably. It's all about fine motor control: the more I attempt to direct my thumb and forefinger to make a careful movement (or stay in the same position), the more tremor there is in that digit.
I learned something in the last few days that I want to record, even though I'm still in the phase of trying to figure out instrumentation for my project: When I try to hold my thumb stiffly, it shakes more.
I'm not entirely surprised by this, since I have an "action tremor" that's associated with voluntary control of my finger muscles. It happens both when I direct my fingers in fine motor actions such as texting or folding a piece of paper, and when I hold something that requires finger control. It doesn't happen when I'm mainly using my hands; for instance, when holding something heavy in my palm. But the shake is worse when holding my thumb stiffly than when commanding it to perform an action. This gives me the idea that maybe training myself to use "softer" movements with my fingers will make the tremor less annoying.
In the meantime, I'm going to use the "rigidity response" to help me with my measurements. One of the hard things about this measurement challenge is that I want to induce the tremor when I'm ready to measure it, and yet I want to track its worsening or improving over time. That means that my method of inducing/measuring the tremor has to stay constant. Knowing that thumb rigidity always produces a good strong tremor is helpful. I've adjusted my way of holding the phone. I'll post a picture when I have somebody nearby to take it. Using a stiff thumb produces a much stronger tremor. (Wiggle at the end is when I'm stopping the measurement.)