This paper describes a sensor that answers to a need of accuracy, stability and low cost for constant-level balloon experiments. The same type of sensor can be employed for any level up to 10 kPa (100 mb) and we hope for an extension up to 1 kPa (10 mb). We review more particularly the aging, temperature effect and air safety tests for the 20 kPa (200 mb) sensor, concluding that 5 × 10−2 kPa (0.5 mb) accuracy is obtained over a six-month period with an instrument that complies with air safety standards. Abstract This paper describes a sensor that answers to a need of accuracy, stability and low cost for constant-level balloon experiments. The same type of sensor can be employed for any level up to 10 kPa (100 mb) and we hope for an extension up to 1 kPa (10 mb). We review more particularly the aging, temperature effect and air safety tests for the 20 kPa (200 mb) sensor, concluding that 5 × 10−2 kPa (0.5 mb) accuracy is obtained over a six-month period with an instrument that complies with air safety standards.