Tone are not calibrated and depend on battery voltage
+4dBu is 3.472Vpp, this cannot be provided by 2 x 1.5 Volt battery...
- The amplitude depends on battery voltage, my measurements 1 kHz
@3Vdc +4dBu = 3.18 Vpp should be 3.472Vpp
0dBV = 3.0 Vpp should be 2.828Vpp
-50MIC = 300-400 mVpp should be 6 if dBu or 9mVpp if dBv,
see also -50MIC waveform +4dBu meas 3.36 Vpp should be 3.472Vpp
@2.5Vdc +4dBu meas 2.66 Vpp should be 3.472Vpp
Tone are square wave, very annoying to listen to......
They should have used a 4.5V supply, and calibrated the Tone output or made it fixed. and least added a low pass filter......
No low batt detection
I Would have paid dobble for these features