INA219 common GND?

[uzer123]

I want to measure current at a custom circuit i have designed. I power the device using a li-ion battery.
I power the device with the battery and put the INA219 in series with the battery positive terminal..
I use an Arduino Uno to measure currect (arduino is NOT part of the custom circuit and i use it only for the measurement).
Do i have to connect all GND between arduino and battery as this image https://cdn-learn.adafruit.com/assets/a ... 1378995140? Arduino is powered by USB.
My logic says, that INA219 measurement (voltage of its shunt resistor) doesnt have to do anything with the circuit under measurement..thus, i do NOT have to connect Arduino-INA gnd with battery-my_custom_circuit gnd...

edit: after reading little of INA datasheet https://www.ti.com/lit/ds/symlink/ina21 ... 252FINA219 i think i HAVE to tie all GND together, because "Bus voltage is measured from Vin- to GND"

[adafruit_support_bill]

Yes. All measurements are relative to the ground.