The test-strip method is the turf-native default: spray a measured strip, catch the volume, and divide. It works for a hand-gun or a boom and needs no nozzle-spacing assumption. The boom formula mode is a second path for ag-style users with a known nozzle output, speed, and spacing.

test-strip:
  pass area    = width × distance   (or a measured area)
  rate/1,000   = volume ÷ (pass area ÷ 1,000)

equivalent GPA (both modes):
  GPA          = rate/1,000 × 43.56     (43,560 sq ft/acre ÷ 1,000)

boom formula (Sprayer Guru):
  rate/1,000   = (136 × GPM) ÷ (MPH × spacing_in)
  OPM input first: GPM = OPM ÷ 128

target check (±5% tolerance):
  deviation %  = (rate − target) ÷ target × 100
  |dev| ≤ 5 → on target · > +5 → over · < −5 → under

walking pace (display only, when time given):
  pace mph     = distance ÷ time × (3600 / 5280)

Worked example (test strip): 1.5 gal over a 7 ft × 143 ft pass = 1,001 sq ft → ≈ 1.50 gal / 1,000 sq ft (≈ 65 GPA), matching Holganix's 1.5 gal/1,000 target. Worked example (boom): 0.44 GPM at 4.5 mph on 20-in spacing → (136 × 0.44) ÷ (4.5 × 20) ≈ 0.66 gal / 1,000 (≈ 29 GPA); a clean set 0.2 GPM at 3.0 mph on 20-in → ≈ 0.45 gal/1,000.

136 is the published (rounded) boom constant from Sprayer Guru — the exact unit-collapse is 12000 / 88 ≈ 136.36, about 0.27% off, well inside the ±5% calibration tolerance the tool itself enforces. The ÷ 43.56 GPA bridge and the × 128 fl oz/gal and OPM/GPM bridges are standard. The ±5% "within 5 percent … calibrated accurately" window is closed at the edges (an exact ±5.0% reads as on target). The double-overlap note stays advisory — the tool never auto-halves your rate. Math follows Holganix, Pesticide Environmental Stewardship, and Sprayer Guru (see Sources below).