I spotted this pattern last year planefagging, and we came to the conclusion that the plane is testing and calibrating avionics, radar, GSP, etc. That's Raven Rock near the center of the semicircle, and Letterkenny Army Depot, where they test missile systems and radar support.
They've had water and wind powered grist mills for centuries in Europe, and up till yesterday, people just washed clothes once a week, on Mondays. Having lots of kids helped to do work around the house instead of spending all their time instagramming and stuff.