An easier constant to prove is the constancy of the weight of the things carried in my car.
My husband calls it the Junk-Mobile, not because she is a junky car, mais non, she is a fine car, she just holds all the errands that I must run in the course of a week:
Junior prom dress to the cleaners, discount trousers to be hemmed, food to food pantry, packages to be mailed out, emergency bag, snacks and water stash (in case of emergency, we have all heard about the lady who survived on a LifeSaver and a stick of gum for three days), books to return to the library….
I have never weighed them physically but know that psychically they tether and weigh on me; I also know that as my car empties of its current errands, more will take their place, keeping the car and me on track and anchored, and the weight of the world, constant.