The dosage volume serves as intermediate storage for the gas pressure from the regulator block's dosage regulator. When the diver exhales, this amount of gas (overpressure) is transferred to the breathing circuit's breathing side.

The amount of gas pressure dispensed into the circuit is proportional to the preceding inhalation volume (the diver's activity). (The value of this proportionality is called dosage ratio and is set using the dosage selector.)

The dosage selector can be set in two different positions marked with a RED and GREEN colour code.

The dosage is optimised for the two standard gases GREEN and RED gas, and their expected diving times for each depth range.

For the “RED” setting the button must be flush with the retaining ring and for the “GREEN” setting the button should be set to be “deeper” inside the retaining ring and with the pin pointing to the relevant coloured mark. This is to ensure you can check the setting without any vision (darkness). When the IS-MIX is properly pressurised, the button cannot be moved.