Leather stitching, whip plaiting, Turk's heads, paracord bracelets and handle wraps, the guides, the tools, the video shelves. All free.
Balloon count: a starting point — the community guides say 8–10 a foot plus 2–7 small fillers, so run your past build's number instead. The mix is the community calculator's default (sourced); the shares go whole by the largest remainder, the total exact (Hamilton's method).
Layers of four sit 0.841·d apart — derived: the next layer rests turned 45° in the hollows, and the height between layers is √(1 − 0.541²)·d. Sourced community check: classic arches run 6 eleven-inch and 12 five-inch a foot, within 5% of this. The layers round up so the build is never short.
Sempertex 11 in = 0.41 cu ft, 16 in = 1.48 (sourced, BalloonBuilder's calculator); Qualatex 11 in ≈ 0.5, 16 in ≈ 1.5 (sourced, to confirm on each maker's chart). Cubic feet left ≈ rated × gauge ÷ full pressure — derived, slightly low at part pressure: helium compresses. Hi-Float: 96 oz treats 567 eleven-inch (sourced).
These three run the same arithmetic the app's engine unit-tests. The app adds the order sheet, the stock and the bags, the quotes and the labels — on the device, offline.