ESP32 ADC reading
On an Uno this is one division and needs no tool. On an ESP32 the reference is an internal 1.1 V reached through an attenuator you chose, so 4095 means four different voltages — and above about 2450 mV it stops meaning anything at all.
1.950 V
2048 ÷ 4095 × 3.9 V = 1.950 V at the pin
Attenuation — ADC_ATTEN_DB_11, full scale 3.9 V
Resolution — top count 4095
At the pin
1950 mV
One count
0.95 mV
Usable window
150–2450 mV
Full scale
3.9 V
1.950 V at the pin. One count is worth 0.95 mV here, which is the finest change this setting can see — averaging sixteen readings buys you noise, not resolution. And the pin has to be an ADC1 one: ADC2 shares hardware with the radio and returns garbage the moment Wi-Fi is up, which is the single most common “it broke when I added Wi-Fi”.