By “Add some quick independent variables through an Apple watch Interface” do you mean just have an interface for recording metrics in general from Apple Watch, or specifically for experiment targets?

It would be great to be able to use the apple watch to track some quick variables during the day. I think two implementations would be very useful: 1. Setting some sort of ‘apple watch reminder’. For instance: Everyday at 12:00 my apple watch asks me what my mood is on a scale from 1-5. Or: my apple watch asks me every 3 hours between 8:00 and 21:00 if I had a headache in the last 3 hours. 2. Having a complication in watch face, or another way to quickly access a metric I want to track as it comes up during the day. For instance: every time I have a cup of coffee I can log it in a few seconds on my Watch. I have found no other app so far that is offering something like this, would be very useful imho.