| Δ0 | walking barefoot on grass itself | walking barefoot on a lawn, strolling barefoot across a grassy park |
| Δ1 | other barefoot activities on natural outdoor surfaces | barefoot walking on sand, on dirt trails, on soil in a garden, on a forest path |
| Δ2 | barefoot activities on indoor or man-made surfaces | walking barefoot on carpet, on wood floors, on tile, barefoot yoga at home |
| Δ3 | other light, low-impact exercises done with footwear | walking in sneakers, gentle stretching, casual cycling, slow jogging |
| Δ4 | other outdoor leisure activities unrelated to footwear | gardening, picnicking, bird watching, sunbathing |
| Δ5 | everyday indoor activities essentially unrelated to exercise or feet | reading a book, watching television, cooking dinner, doing laundry |