deviceSrate

The rate the device is sent, and so streams at: srate, except in an impedance mode the firmware cannot measure at that rate, which streams at 250 Hz instead. The firmware takes each electrode's impedance as max − min over a fixed 20 samples, which spans a flip of the square test wave only while half the wave's period is longer: ImpedanceMode.HZ_7_8 up to 250 Hz, ImpedanceMode.HZ_31_2 up to 1 kHz. Faster, a lifted electrode can read close to 0 kΩ. ImpedanceMode.DR_DIV4's wave follows the rate, so it is never capped. srate itself is kept, so turning impedance off gives the set rate back.