DragTree simulates a real NHRA Christmas Tree (drag strip starting lights) and uses your phone's accelerometer to measure reaction time to the millisecond — no tapping required. Mount your phone on the dash, stage up, watch the tree, and floor it. The app detects launch G-force automatically and records your RT. Fully offline — no internet, no account, no ads. TREE MODES • Pro Tree (.400s) — all three ambers fire simultaneously, green follows 0.400s later • Sportsman Tree (.500s) — ambers count down one at a time, green follows 0.500s after the last amber REACTION GRADING • Perfect: 0–0.049s • Pro: 0.050–0.099s • Great: 0.100–0.199s • Good: 0.200–0.349s • Late: over 0.349s • Red Light: launched before green FEATURES • Accelerometer launch detection — rolling baseline, no calibration step • Three sensitivity presets: Gentle (0.15g), Normal (0.25g), Hard (0.46g) plus custom dial • Session history — last 30 runs, personal best highlighted • Reaction time trend chart — bar chart of recent runs • Series mode — run 3, 5, or 10 back-to-back stages with avg RT, best/worst, and consistency score • Optional audio cues — amber click, green chirp, result ping, red-light buzz • Diagnostics screen — live G-force, sensor telemetry, last-launch breakdown • Browser / simulator mode — on-screen FLOOR IT button for desktop practice PERMISSIONS • HIGH_SAMPLING_RATE_SENSORS — required for 125 Hz accelerometer sampling. No other sensor or location permissions used. No internet connection required after install.