The difference will be : $$\Delta M=V*(\rho_{He}-\rho_{air})$$ where $\rho$ stands for the volumetric mass density and $V$ the volume inside the canister. Therefore $V*\rho_{air}$ is the mass of air inside the canister.

The scale measures the difference between the weight of the canister and the gaz inside and the weight of the same volume or air (archimedes).

The difference will be : $$\Delta M=V*(\rho_{He}-\rho_{air})$$ where $\rho$ stands for the volumetric mass density and $V$ the volume inside the canister. Therefore $V*\rho_{air}$ is the mass of air inside the canister. $$M_{displayed}=V_{inside}*\rho_{gaz}+V_{canistersteel}*\rho_{steel}-V_{tot}*\rho_{air}$$

The scale measures the difference between the weight of the canister and the gaz inside and the weight of the same volume of air (archimedes).

The difference will be : $$\Delta M=V*(\rho_{He}-\rho_{air})$$ where $\rho$ stands for the volumetric mass density and $V$ the volume. Therefore $V*\rho_{air}$ is the mass of air inside the canister.

The mass of air inside the canister is usually neglected, but it is measured nonetheless with the scale.

The difference will be : $$\Delta M=V*(\rho_{He}-\rho_{air})$$ where $\rho$ stands for the volumetric mass density and $V$ the volume inside the canister. Therefore $V*\rho_{air}$ is the mass of air inside the canister.

The scale measures the difference between the weight of the canister and the gaz inside and the weight of the same volume or air (archimedes).