Strobe tachometer (RPM meter)

STROBE TACHOMETER lets you measure rotation speed by matching flicker frequency to the object's rotation. It includes Laser Tachometer and Magnetic Tachometer modes with high precision: Laser range 0.3 Hz (18 RPM) to 1000 Hz (60,000 RPM) with 0.01–0.0001 Hz steps; update time 1 s; 5 mW laser power. Magnetic range 0.1 Hz (6 RPM) to 45 Hz (2,700 RPM) with 0.2–2% steps; update time 2–5 s. You can adjust frequency by long-press; the display can show Hz or RPM; you can change speed with app settings and the flicker frequency can be displayed in Hz or RPM.

For speeds beyond the upper limit, you can determine the speed by measuring at a lower flicker frequency and applying a simple calculation described in the appendix. The image is sharper in low light, and the iPhone flashlight can run up to 100 Hz (6,000 RPM) while a connected flashlight supports up to 1000 Hz (60,000 RPM). Overheating may cause the iPhone flashlight to turn off automatically.