I was unaware that context would not be able to provide enough clarity...
I am not a tube for dispensing filth, as I am a person. However I also do not live in the year 1300 and I'm not a servant.
I sew things, with a sewing machine, and therefore because I do not own a scale I will use the measurements of my body, as they are located for sewing purposes (waist is not at your belly button, but is the narrowest portion of your torso, or where the crease forms if you bend sideways), to see if commuting is benefiting me physically.